$3\mathrm{.}8.$ An F$-15$ supersonic fighter aircraft is in a

rapid climb. At the instant it passes through a

standard altitude of $25,000ft,$ its time rate of

change of altitude is $500f\frac{t}{s}.$ Corresponding to

this rate$-$of$-$climb at $25,000$ ft is a time rate of

change of ambient pressure. Calculate this rate

of change of pressure in units of pounds per

square foot per second.