If a * b = a - 3b and a # b = 2a + 3b, evaluate the expression (4 * 3) # 5.
If y # y = 2x + 3y and x * y = 5x + 4y, evaluate the expression 2 # (4 * 3).
Please help! Try to explain how I should solve these - don't just give me the answer. These problems showed up in my math book, and my teacher didn't teach us how to do those in the lesson. And, first of all, what does # mean in a problem like this? Thank you.