51:15 The model shows the expression 21 + 9.

A model with 3 rows of 7 squares and 3 rows of 3 squares.

Which expression is equivalent to this sum?
3 (7 + 3)
3 (7) + 3
3 + 7 + 3
7 (3 + 3)

need more information

step-by-step explanation:

answer: check all that apply, where the options?

step-by-step explanation:

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!

loloo

step-by-step explanation:

lololool