The amount of lemonade is y and the time since the leak started is x, then y=mx+c where m=-3, the rate at which the lemonade is leaking, and c=32, the amount of lemonade initially.
So y=32-3x. The x intercept is when y=0, so 3x=32 and x=32/3 minutes=10m 40s. This means it takes 10 minutes 40 seconds for all lemonade to leak out.