Mike and bill sell cars for jangle's auto. over the past year they sold 640 cars. assuming mike sells 3 times as many as bill, how many cars did mike sell?

Over the past year they sold 640 cars. Assuming Mike sells 3 times as many as Bill:

x --> cars sold (by Mike)
y --> cars sold (by Bill)

x + y = 640
x = 3y

3y + y = 640
4y = 640 |:4
y = 160

x = 3y = 3 * 160 = 480

Mike sold 480 cars and Bill sold 160 cars.