Im trying to learn how to solve myself so please tell me how you found answer

8

Step-by-step explanation:

We can set this up in a ratio. In the picture shown, there is a large triangle and a small triangle inside it.

The ratio for the large triangle would be 21/28.

I got the '21' from '21/28' from doing 15+6.

Now the ratio for the small triangle is 6/x. As x is the unknown value.

To find x, we have to cross multiply and to do that we would do:

21x = 28x6

Simply and you get

21x=168

x=8

Hope this helps! :)

c.

step-by-step explanation:

she should of added 9^2 and 12^2. that is because it is a^2+b^2=c^2. c^2 is the hypotenuse and should always be bigger than the other two numbers. which is why she should of added 9 squared and 12 squared together instead of 15 squared.