(a)[2]
Solve the equation $5x + 6 = 3x$.
(b)[3]
A plum has mass $n$ grams. An apple has twice the mass of the plum. A banana has a mass that is $50$ grams greater than the mass of the apple. The combined mass of the plum, the apple and the banana is $450$ grams. Form an equation in $n$ and solve it to determine the mass of the plum.
(c)[3]
Use factorisation to solve $x^2 - 4x - 21 = 0$.