Answer:
D
Step-by-step explanation:
R(x) = -x^2+122x+400
224
a = -10
-0.4a + 3 = 7
subtract 3 from each side
-0.4a + 3-3 = 7-3
-.4a = 4
Divide each side by -.4
-.4a/ -.4 = 4/-.4
a = - 10