Can someone please tell me what I am doing wrong with the following problem. The computer keeps telling me that I am coming up with the wrong answer.

In a constant-volume gas thermmoeter, the pressure at 18.0 C is 0.980 atm. What is the pressure at 42.0 C?

I am using the equation (P1/T1) = (P2/T2) and I am solving for P2.

(P1/T1) = (P2/T2)

P2 = (P1/T1)(T2)

P2 = (0.980/18.0)(42.0)

P2 = 2.29 atm

I know this is a really simple problem, but I just don't understand what I am doing wrong. Someone please help me.