10(6-x)+x+ 18 = 10x+(6-x)
2. If the number of cantaloupes is x and the number of watermelons is 2x, it will take x/40 days to sell out cantaloupes.
2x-x/40×50=360
3. Let Qian Ming be X yuan, then Sean is 0.25x+60.
x+(0.25x+60)= 1280
How to solve the equation is up to you.