Can someone explain this to me? i don't understand median mean and mode. : d (don't mind about the rest of the page, just look at #2.)

P= $1400,300 r = 7 1/2% t = 4 what is i ? $4.29 $429.00 $4290.00

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?

The fence around a quadrilateral-shaped pasture is 3a^2+15a+9 long. three sides of the fence have the following lengths: 5a, 10a-2, a^2-7. what is the length of the fourth side of the fence?