How to add 2 column values and find out percentage value?

When I do df, I get folowing results:

Filesystem     1K-blocks     Used Available Use% Mounted on
udev             1529860        4   1529856   1% /dev
tmpfs             308116      960    307156   1% /run
/dev/sda1       47929224 40768468   4703004  90% /
none                   4        0         4   0% /sys/fs/cgroup
none                5120        0      5120   0% /run/lock
none             1540572       76   1540496   1% /run/shm
none              102400       44    102356   1% /run/user
Shared         168479740 78002196  90477544  47% /media/sf_Shared
/dev/sr0           83904    83904         0 100% /media/amitk/VBox_GAs_6.0.41
 

Now, I want to add the value of "1K-blocks" and "Used" for sda1 and Shared, in order to calculate the ratio of the sums, and store them in a file EmmcSpace.txt.

• In the above example, ths sums for "1K-blocks" would be 47929224 + 168479740 =216408964, and for "Used" 40768468 + 78002196 = 118770664.

• I then want to do (118770664 *100)/ 216408964=54.88 and store the result in the file.

But I am stucked with this calculation part.I don’t want "use%" column for some reason. So how do I move ahead so that finally in the EmmcSpace.txt file there should only percentage value i.e. 54.88 or 54 and nothing else

#include<stdio.h>
    #include<unistd.h>
    #include<string.h>
    int main(void)
    {   
        system("df |grep sda1 |awk -F ' ' '{print $2, $3}' >EmmcSpace.txt");
        system("df |grep Shared |awk -F ' ' '{print $2, $3}' >>EmmcSpace.txt");
        
        system("awk '{total1 = total1 + $1}END{print total1}' EmmcSpace.txt >>EmmcSpace.txt");
        system("awk '{total2 = total2 + $2}END{print total2}' EmmcSpace.txt >>EmmcSpace.txt");
        
        //system("awk '{printf  (($total2 *100) / ($total1))}' EmmcSpace.txt");
        //system("total='expr $total1 * 100' '{print total}'");
        //system("total=`expr $total1 * 100` ");
        //system("total=`expr $total / total2`");
        
        return 0;
    }
    

df | awk '$1~/^Shared/ || $1~/^/dev/sda1/ {total+=$2;used+=$3} END{printf("%.2fn",100*used/total)}' > EmmcSpace.txt