Let a Firm Use Labor (L) and Capital (K) as Its

Multiple Choice

Let a firm use labor (L) and capital (K) as its only inputs to produce an output, Q. The cost of labor is w = $5 per labor hour and the cost of capital is r = $15 per machine hour. When capital is measured on the vertical axis and labor on the horizontal axis, what is the slope of an isocost line for this firm?

A) -3.
B) -5.
C) -15.
D) -1/3.