7(15) = 105
10% off means u r paying for 90%...
0.9(105) = 94.50 <=
Each book costs $15. since he had 18 dollars left, you can subtract 18 from 108. then divide that answer by 6. 90/6 = 15.
Hope that helped!
Answer:
By the Pythagoras theorem, the hypotenuse (c), is equivalent to:
a^2+ b^2= c^2 where a and b are the other two sides of the right angled triangle, hence c= square root (15^2+ 20^2)= 25
