Question 974793
x, edge of small square
4x/3, edge of big square


{{{x^2+(4x/3)^2=900}}}


{{{x^2+(16/9)x^2=900}}}


{{{(25/9)x^2=900}}}
{{{(5/3)x=30}}}
{{{x=30*3/5}}}
{{{highlight(x=18)}}}