A triangular plot covers 216 square metres, and its height is three-quarters of its base. How long is the base, in metres?

Write the height as $0.75b$. Then (1/2) $xbx0.75b=216$ gives $0.375b^2=216$, so $b^2=576$ and $b=24$ m. (The height is 18 m, and $(1/2)\times 24\times 18=216$.) The trap 18 quotes the HEIGHT, which the question did not ask for; 16.97 drops the 1/2, solving $0.75b^2=216$ to get $b$ = √288; 12 halves the correct base, applying the 1/2 a second time at the end.