The difference between three times a number and 15 is equal to 6. find the number

15+6=21
21÷3=7
answer
3×7-15=6

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.