I am totally horrible at geometry! can someone help me please

Answer: 6
Step-by-step explanation:
We will set up a proportion to solve. Let x be equal to ?.
[tex]\displaystyle \frac{3}{5} =\frac{x}{x+4}[/tex]
Now, we will cross-multiply.
3 * (x + 4) = 5 * x
3x + 12 = 5x
12 = 2x
6 = x