f(x)=x^2 +8x
f(d-3) basically what we get from this is that the x value is d-3
to find f(d-3) simply plug in d-3 for every x
f(d-3)=(d-3)^2 + 8(d-3)
that would be one form of the answer, but we can also continue multiplying it out
f(d-3)= d^2-6d+9+8d-24
add like terms
f(d-3)=d^2+2d-15
have a nice day and i hope this helps :)
