7. Let x be the length and y be the width. The perimeter can be worked out by adding twice the length (2x) and twice the width (2y)
y = 12 (given from question), 2y = 24
2x + 2y = 68
2x + 24 = 68
2x = 68 - 24
2x = 44
x = 22
The length is 22 cm.
9. 100% as a decimal number is 1. 85% is 0.85. 25% is 0.25. Therefore 200% would be 2. and 225% would be 2.25. Your answer is 2.25.
10. 9/5 as a decimal is 1.8. You can work this out by using bigger numbers and messing about with the decimals. For example, 90/5 is 18, which is a whole number. However, that's not the question (they asked for 9, not 90), but 90 is just 9 multiplied by 10, so I can just do the opposite for the answer. I divide 18 by 10, which is just 1.8.