A right triangle has hypotenuse 25 cm. One leg has length x cm and is increasing at 3 cm/s, while the other leg adjusts so that the hypotenuse length remains 25 cm. For what value of x is the area of the triangle neither increasing nor decreasing?
a) 21.2 cm
b) 17.7 cm
c) 12.5 cm
d) 15.0 cm