#1**+1 **

The notation "~" means similar. This can help with the problem.

First, we need to find the scale factor of the two triangles. This is 30 / 18 = 5 / 3 (to get from the smaller triangle to the bigger one)

Therefore, we can say that:

5 / 3(x + 1) = 2x - 1

5 / 3 x + 5 / 3 = 2x - 1

5 / 3 = 1 / 3 x - 1

8 / 3 = 1 / 3 x

x = **8**

**We can also prove this backwards (AKA check our work)**

2(8) - 1 = 15

x + 1 = 9

5 / 3 (9) = 15

And, we can see that our answer is right! (more of "my" answer, but "our" just sounds less narcissistic than "my": unless you already solved the problem, and got the same answer, but I doubt that since you posted this question)

:)

ilorty Aug 29, 2020