Question 1077822
x, base of rectangle
{{{x-x/5}}}, altitude of rectangle



{{{x-x/5=5x/5-x/4=4x/5}}}


{{{highlight_green(2(x)+2(4/5)x=18)}}}


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{{{x+4x/5=9}}}

{{{5x+4x=45}}}

{{{9x=45}}}

{{{highlight(x=5)}}}
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altitude is {{{(4/5)x=(4/5)*5=highlight(4)}}}.