Li Hui went to Yuquan brand clothing store to do social investigation. She learned that in order to motivate the sales staff, the mall implemented the method of "total monthly income = basic salary+piece rate bonus" and obtained the following information:

Assume that the number of pieces sold per month is X, and the total monthly income is Y yuan. For each piece sold, a reward is A yuan, and the monthly basic salary of sales staff is B yuan.

(1) Find the values of a and b;

(2) If the monthly income of Xiao Li, the shop assistant, is not less than 1800 yuan, how many clothes will Xiao Li sell this month at least?