To factorise and solve for x, open two sets of brackets, i.e: (x )(x ). For this question note than one x should be replaced by 2x such that (2x )(x ). List the pairs of numbers that give a product of 12, i.e: 1 and 12, 2 and 6, 3 and 4. As 12 is minus in this equation, note that one number in each pair will need to be negative in order to make 5x. Now substitute each pair into the brackets to see what makes the correct equation. End up with (2x-3)(x+4). Now equate each bracket to 0 to find x:2x-3=0 -> 2x=3 -> x=3/2 and x+4=0 -> x=-4. So x=3/2 or -4.