Where is 'd' a minumum? (this is basically pythagorean theorom)
d = sqrt( 22500t^2 + 225 +160000t^2 - 12000t) This is a quadratic equation.....
(1) d^2 = ( 182500t^2 -12000t + 225) find the minumum....take the derivative and look for slope = 0
365000t - 12000 = 0
t = .032876 hr
Substitute this value in to the 'd' equation
d = sqrt ( 150 (.032876))^2 + (15 - 400(.032876))^2 ) = 5.2668 miles
Or take equation (1) and graph it to find the minimum point of the parabola......