If a guardrail is to be placed around the edge of a circular swimming pool with a diameter of 21 ft, how many feet o railing would be needed? Use 22 7 for TT.​

On number 10, you know that the whole side length is going to be 1/4 of 48 because 9 * 4 = 36. So, you can say that x will be equal to 12, since 1/4 of 48 is 12 and 12*2 + -12 = 12. 

On number 11, you can say that 5x +5 = 40 because that is 5 times 8. So, you can solve for this to get x = 7 by subtracting 5 from both sides and then dividing both sides by 5. Hope this helps and let me know if you have more questions!