How do I find the temperature measured at 350 hPa?

1. You are flying 2.5 km over the ground while your mates are flying up at 350 hPa. All the way between you there are clouds. If you measure that the temperature outside is 4 celsius, what temperature do they measure?

Don’t really know where to start, to be honest. I don’t find an equations in my book that seem reasonable to solve this task.

2. You are in an airplane 2.5 km above the ground. Assume that the atmosphere can be treated as a Standard Atmosphere. The temperature outside is 4 Celsius. You look down toward the ground and see no clouds. What is the expected temperature of the ground?

Should I just use the adiabatic lapse rate?