Question

A gas sample’s volume changed from 102 L to 75 L when the pressure was changed to 28.0 lb/in2 with a constant temperature. What was the starting pressure?

Answer 1

We see here that the temperature is constant here so we can apply Boyle's law here which say that

$pV=constant\\p_1V_1=p_2V_2\\p_1\times102=28\times75\\p_1=20.59\ lb/in^2$