You can
put this solution on YOUR website!I think you are getting confused in reading your problem.
The pressuse is 25 lb per sq. in. not (25 lb/in)^2.
The volume is 400 cubic ft. not (400 ft.)^3.
So you have in place of P = k/V the following:
25 = k/400
k = 10,000
The equation you want is P= 10,000/V
Now, find the pressure when the volume is 150 cu. ft.
P = 10,000/150= 66 2/3 lb./sq.in
Cheers,
Stan H.