How to show that $|P(A\cap B)−P(A)P(B)|≤\frac{1}{4}$?

Question

I am trying to show that $$ |P(A\cap B)−P(A)P(B)|≤\frac{1}{4} $$ But I don't see how to begin... If $A$ and $B$ are independent the result is obvious. Can someone give me a hint?