Answer: Choice (B)
25b^2+40b+23
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Work Shown:
c(b) = 5b
h(b) = b+4
h(c(b)) = c(b)+4 ... replace every b with c(b)
h(c(b)) = 5b+4 ... replace c(b) on the right hand side with 5b
For the sake of simplicity, let's call "h(c(b))" as k
k = h(c(b))
k = 5b+4
that way we can use it later in the next section
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a(b) = b^2 + 7
a(k) = k^2 + 7 ... replace b with k
a(k) = (5b+4)^2 + 7 ... plug in k = 5b+4
a(k) = 25b^2+40b+16+7 .... use FOIL rule
a(k) = 25b^2+40b+23
a( h(c(b)) ) = 25b^2+40b+23
In that last step, I replaced k with h(c(b)) so that we get to the original format your teacher wanted.