Let's represent the unknown number with Y So it says 5 times the sum of Y plus 3 equals 8 times Y minus 9 That is represented as; 5(Y+3)=8Y-9 First of all, multiply 5 by what is in the bracket. That will be 5Y+15 (5 times Y is 5Y and 5 times 3 is 15) Therefore; 5Y+15=8Y-9 Collect like terms. So -9 will go over the equality sign to become +9. The same applies to 5Y 15+9=8Y-5Y 24=3Y Divide both sides by 3 24 divided by 3 is 8. So Y= 8 The number is 8 which is B