Question

if f(x)=3x+5,evaluate f(7) - f(5)

Answer 1

=3x7+5 - 3x5+5
=21+5 - 15+5
=26-20
=6

Answer 2

$f(7) = 3(7) + 5 \\ \: \: = 21 + 5 = 26 \\ \\ f(5) = 3(5) + 5 = 15 + 5 = 20 \\ \\ f(7) - f(5) = 26 - 20 = 6$