I need some assistance in slopes and this app

On monday,mrs.wise bought 3 lbs of apples at $4per lb= 4*3=$12on tuesday ,20%off and she buy 5 lbs of apples = $4-20%=3.20*5lb=$16example: other wise when she buy 5lbs on monday she have to spend 4*5=20

I'm gonna have to say about 13 percent

Ifound this on google “that means that the graph of a function with direct variation has these features: it is a straight line: because the slope is the ratio y/x = k. it passes through the origin (0,0): because y = kx = k (0) = 0.” i hope this you for what your looking for