Let's use the line on the right side. In the smaller triangle, the length is 4. The same side on the bigger triangle is 12. The ratio of the smaller triangle to the bigger triangle is:
[tex] \frac{4}{12} \rightarrow 4:12 [/tex]
[tex] 12 \div 4 = 3 [/tex]
To find a side length for the bigger triangle, all you need to do is multiply by 3. The same side on the smaller triangle is 5. Multiply by 3
[tex] 5 \times 3 = 15 [/tex]
That means x = 15
