Question

the equations of two functions are y equals -21x + 9 + y equals -24x + 8 which function is changing more quickly and why?

Answer 1

By "-21x + 9 + y equals -24x + 8" I'm assuming you meant

"y = -21x + 9 AND y equals -24x + 8." Using " + " to indicate "and" could be confusing.

We then have the system of linear equations

y = -21x + 9

y = -24x + 8

The function with the greater slope is the 2nd: y = -24x + 8 (with the understanding that we're focusing on the magnitude of the slopes). Thus, it is this function that changes more quickly.