A man at the fair in Kilkenny Bought a number of twigs for a penny Just nine times the square Of the twigs he bought there Is half of their cube so how many?

you can write this as the equation: 9 n n = 1/2 n n n where n is the number of twigs multiply both sides by 2, and cancel 18 n n = n n n by inspection, n = 18 QED