Primary school sixth grade mathematics problem 100, urgent

Primary school sixth grade mathematics problem 100, urgent

8 times of a number minus 5 times of this number, the difference is 21.9, find this number. What number of 4 times minus 5.4 and 0.6 product, the difference is 1.72? A number of 3 times plus 1.5 times of this number equals 22.5, how much is this number? 51 divided by 4.8 quotient minus 0.72, what is the difference? 1.5 and 7.5 sum, and then multiply by 0.82, product