A line passes through the origin and the point (5,3). It also passes through (n,18) What is n?

Can someone me with this graph problem by the way i need to know the answers by today since this assignment is due ! !

Cherie works in retail and her weekly salary includes commission for the amount she sells. the equation s=400+0.15c models the relation between her weekly salary, s, in dollars and the amount of her sales, c, in dollars. interpret the slope of the equation.

If f(x) = 4 - xand g(x) = 6x, which expression is equivalent to (g-1)(3)? 6-3-(4 + 3)2 6-3-(4-32) 6(3) - 4+32 6(3)-4-32