Consider a market with market demand curve Q=100-P. The inverse demand curve is P=100-Q. [For a demand curve P=a-bQ, the marginal revenue curve is P=a-2bQ.]

Suppose that there are two firms, A and B, in the market each with marginal cost MC=10. There are no fixed costs. The two firms compete by setting quantities simultaneously. If firm A were to produce qA=20, what would firm B's best response be (in terms of quantity)?

Please help if the correct answer is 35 based on B's response curve.