Hello!
Plug in the value of x:
f(x)=5(x-3)+17
f of x is 5 times the difference of x and 3 plus 17
plug in 2:
f of 2 is 5 times the difference of 2 and 3 plus 17
f(2)=5(2-3)+17
f(2)=5(-1)+17
f(2)=-5+17
f(2)=12
Hope everything's clear.
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