First we know that a perpendicular line is one that intersects at a 90-degree angle. This is simply the negative inverse of the slope in our case. So, 4 turns into -1/4 and that is our new slope. Next we know that we want it to pass through the point (6,1). Right now our equation is y = -1/4x + b. We can plug (6,1) into this equation and solve.
1 = -1/4(6) + b
1 = -6/4 + b
4/4 + 6/4 = 10/4
10/4 = b
simplify: 5/2 or 2.5 = b
Now we have our y-intercept, so we can complete our equation.
We have the growing function f(x) = 86.(1.18)x. If we want to write f in terms of z, we need to consider that x = z/7, since there are 7 days in each week. Then,
