Mints cost 5 cents each and gumballs cost 3 cents each. Kathleen spent 60 cents buying x mints and y gumballs.

Slope intercept form:
y=-5/3+20

What is the slope and what does it represent in this problem?

since you left out the x, I'll guess.

The slope doesn't really mean anything useful in this situation. It's the price ratio between mints and gumballs, and is negative since the more mints she buys, the fewer gumballs she can afford.