What is systems of linear equations

In mathematics, a system of linear equations is a collection of one or more linear equations involving the same set of variables. For example, is a system of three equations in the three variables x, y, z.

Example:

x + z = 6.

z − 3y = 7.

2x + y + 3z = 15.

answer: 21$

step-by-step explanation:

$42 / $14 = 3   (ratio 3: 1)

$7 x 3 = $21

i belive those are the ones that are under 90 degreese.