Hey Nora314.

Hint: Write down all possible pairs of values where X + Y <= 10 and use the fact that P(A = a, B = b) = P(A=a)*P(B=b) for independent random variables A and B (with corresponding events a and b respectively).

To keep track of things, I suggest you write the pairs with the corresponding probability.

After this, you should be able to get the final answer.