Suppose x is the price before lunch, y - after. Then we get the following equations: ax + (10-a)y = 3500; bx + (16-b)y = 3500; cx + (26-c)y = 3500 Which is eq

Suppose x is the price before lunch, y - after. Then we get the following equations: ax + (10-a)y = 3500; bx + (16-b)y = 3500; cx + (26-c)y = 3500 Which is equivalent to (assuming x = y + d): ad + 10y = 3500; bd + 16y = 3500; cd + 26y = 3500