Answer:
y = -0.904, 19.904
Step-by-step explanation:
f(y) = 9
f(y) = sqrt(y + 99)
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9 = sqrt(y +99) - y
81 - 18y + y^2= y + 99
-19y + y^2 = 18
y(y - 19) = 18
y = -0.904, 19.904
(I used a calculator to solve those values)
