Question 1023390
Your second question:
x is amount of sales;
y is amount of month's pay;
{{{y=0.076x+1540}}}


Let y=4291.2.

{{{0.076x+1540=4291.2}}}
Solve for x.



Your first question:
Use this as guidance for the method...
<a href="https://www.youtube.com/watch?v=VDKztVZUgnM">Equation of Line Through Two Points</a>