To answer this question, one must be familiar with Gay Lussac's Pressure Temperature Law. According to the law: [tex] \frac{P1}{T1} = \frac{P2}{T2} [/tex]
Substituting the values:
Let x be the new gauge pressure.
[tex] \frac{40}{60} = \frac{x}{90} [/tex]
We get x = 60psi.