Cows are fed both grass (X1) and supplements (X2). Average weight gain (Y) is related to the two food sources as follows.

Y = -1.2 + 0.5*X1 + 2.0*X2 - 0.05*X1*X2

What is the marginal effect on average weight gain of supplements (X2) when the amount of the two feeds are X1=10 and X2=2? Put your answer correct to two decimal places.