If we are to establish the equation that would allow us to express the given scenario, we are to first make all the values into a per year or per month basis. For the purpose of showing the solution in this item, we use the per year basis. The equation is then equal to,
P = 450x - (1500)(12)
P = 450x - 18000
The equation is in the slope-intercept form in which the slope is the numerical coefficient of the first term on the right hand side of the equation. Hence, the answer to this item is 450.