Step-by-step explanation:
expand 3x(x+7)
you do this by multiplying 3x by everything in the brackets
=
[tex] {3x}^{2} + 21x[/tex]
expand 4(x+7)
= 4x + 28
add each expanded bracket together
[tex] {3x}^{2} + 21x + 4x + 28 = [/tex]
{3x}^{2}+ 25x + 28
