Question

suppose that y varies directly as x, and y = 15 when x = 4. what is the value of y when x = 9?

Answer 1

"Varies directly" means that whatever happens to x also happens to y, and vice versa

So for a problem like this, you would figure out what you multiply your first x value by to get to your second x value, and then multiply your first y value by that same number to get your second y value