Question

PLEASE ANSWER QUICKLY!!!!!!!!!!!

Answer 1

21

$\frac{1}{2} height \: of \: trapezium(a + b) = area \: of \: trapezium$

half the height is 3

a=7

b=x

3(7+x)=84

21+3x=84

place the like terms on one side

84-21=3x

63=3x

x=21