7. [6 pts] The base 13, and height I1 of a triangle change with time t, at a certain instant the dimensions are 13 = 4cm 1-5 cm and 13 is increasing at a rate of 2 em/s while I] is decreasing at a rate of 1cm/s. At that instant the rate of change of the area of the triangle is Al 3 an /s 1) 4 cm is (15cm /s D) 20 cm /'s [) none of these