Answer:
The value of x is 5.
Explanation:
In order to find the value of x, we first need to find the scale factor. We can find this by dividing any side of the larger triangle with the corresponding part of the smaller triangle.
15/12 = 5/4
This means everything in the larger triangle is 5/4 times as great as the smaller triangle. Knowing this, we can set the larger unknown side equal to 5/4 times the smaller.
4x = 5/4(3x + 1)
4x = 15x/4 + 5/4
x/4 = 5/4
x = 5