1) 5+ m = 8 In order to find the value of m is to get it by itself.
Step 1: Move the 5 to the other side of the equation
5 + m = 8

5 + m = 8

m = 8 - 5

m = 3

for checking

5 + 3 =8

hello from mrbilldoesmath!

answer:

25x^2 + 90x + 84

discussion:

mn(x) = m(n(x)) = m( 5x + 9) =

(5x + 9)^2 + 3 =>

25x^2 + 90x + 9^2 + 3 =

25x^2 + 90x + 84                 (as 9^2 = 9*9 = 81)

which is the second choice

regards,  

mrb

p.s.   i'll be on vacation from friday, dec 22 to jan 2, 2019. have a great new year!