If 3d – (9 – 2d) = 51, find the value of 3d.

3d -(9-2d) =51
= 3d-9+2d = 51
=5d-9 =51
= 5d=60
d=60/5 = 12
 so 3d = 3*12 = 36

When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. if you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term.