The mean of seven numbers is 21. five of the numbers are 18, 23, 21, 17, and 19. one of the remaining numbers is 3/4 of the other remaining number. find the two unknown numbers.

The u-drive rent-a-truck company plans to spend $13 million on 320 new vehicles. each commercial van will cost $25 comma 000, each small truck $50 comma 000, and each large truck  $80 comma 000. past experience shows that they need twice as many vans as small trucks. how many of each type of vehicle can they buy?