What is 3x - 4 + 20 =55

So first subtract 20 from both sides of the equation.
3x-4=35
now add 4 to both sides.
3x=39
now divide both sides by
x=13

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.