What is n+12 ? I need help with this I don’t understand it

The angle of a triangle are given as 6x,(x-3), and (3x+7). find x then find the measures of the angles

Find the value of x for which the lines are parallel.

Isabel graphed the following system of equations. 2x – y = 6 y = -3x + 4 she came up with the solution (2,-2). what were the 3 steps she did to get that solution? (make sure they are in the correct order)