PLEASE HELP!!QUICK! in 3 years ,a gyms membership went up from 6,400 to 8,400.which expression shows how to find the percent of increase? A.2,000 divide by 8,400
B.2,000 divide by 6,400
C.6,400 divide by 2,000

answer: 204

step-by-step explanation:

we are told that the revenue is

x⋅(4080−10x)=−10x^2+4080x

this is a quadratic function, so to maximize it we should find the x-value of its vertex. recall that the x-value of the vertex of the parabola ax^2+bx+c is given by the formula −b/2a.

so in this case, we have a=−10 and b=4080, so the x-value of the vertex is

−b/2a= −(4080)/2(−10)=204