slopes

[skan]

I am having troubel understanding slopes. I know the slope formulas but when given a triangle function, say on the x axis one end of the base of the triangle is at -2 and the other end at 2 and on the y axis they converge at 2.

and given a rect function, and when asked to find the area of overlap between the rect and triangle function, I multiply the amplitude or height of the rect function with what of the triangle function???

thanks a lot.