Question 442578
Recall that {{{(1/2)*b*h = A}}}

We are given that {{{b = 2x+5}}} and {{{h = x}}} and {{{A=84}}}

Then {{{cartoon((1/2)*(2x+5)*x = 84, (1/highlight(2)) *(2x+5) * x = 84, (2x+5)*x = 168, 2x^2 + 5x = 168, highlight(2x^2 + 5x - 168 = 0))}}}
*[invoke quadratic "x", 2,5,-168 ]

So our positive answer is x = 8. This means our height is 8.

What is left to find is the base.

Remember, our base = 2x+5, so plug in x=8 to find the base.

{{{cartoon(b = 2(8) + 5 = 21, b = highlight(21))}}}

So our base is {{{highlight(21)}}}
and our height is {{{highlight(8)}}}