20. isosceles means two sides are the same length, so you take the ten off the perimeter to get 26 remaining cm (36 -10) and you then divide that by two to get both sides of 13 cm (26 / 2)
21. because you know that if you split the triangle down the middle you get a right triangle and you can use a^2+b^2=c^2 to find the height, so we take the one side of 13 cm and half of the third side, which is 5, and you can find your answer (a^2 + 5^2 = 13^2 ---> a^2 + 25 = 169 ---> a^2 = 144 ---> a = 12)
You would have $660. The trick for 10% of something is to move the decimal one place to the left. The decimal is “hidden” to the right of the last 0. Add that interest on to get your answer!! Good luck!
