Can anyone help me use Charles' Law to answer these questions with work, all temp must be in Kelvin?

Question

1)I have made a thermometer which measures temperature by the compressing and expanding of gas in a piston. I have measured that at 1000 C the volume of the piston is 20 L. What is the temperature outside if the piston has a volume of 15 L? What would be appropriate clothing for the weather?

2)How hot will a 2.3 L balloon have to get to expand to a volume of 400 L? Assume that the initial temperature of the balloon is 25 0C.

Answer 1

Temp in K = Temp in C + 273

and use V1/T1 = V2/T2