Step One: Because the amount she is paid is the 25% commission, multiply the 1,631.24 by 4 ( 4 because she is paid 1 out of 4 parts of the total selling price)
Using the formula for slope, we can find out that So -105 is the slope, and because she bought her laptop at $1160, the y-intercept is 1160. This means that the equation is V(t)=-105t+1160.