Using linear equations to solve unknowns in matrices

**Question 87**

Find the solution of the following set of linear equations.

[ 1 2 1 4 ] {x1} = { 13 }

[ 2 0 4 3 ] {x2} = {28.3}

[ 4 2 2 1 ] {x3} = {20.9}

[ -3 1 3 2 ] {x4} = {6.5 }

Just to be clear there are three matrices, of the orders 4x4, 4x1 and 4x1. I've managed to split them into the linear equations, but just looking at them make me sweat with fear.

x1 + 2 x2 + x3 + 4 x4 = 13

2 x1 + 4 x3 + 3 x4 = 28.3

4 x1 + 2 x2 + 2 x3 + x4 = 20.9

-3 x1 + x2 + 3 x3 + 2 x4 = 6.5