Answer: 5
Step-by-step explanation: These two triangles are similar triangles. Since they are similar, they must be scaled equivalently. The scale factor is 5. To know this, 3 times 5 is 15, and being equivalent, we can figure 5 times 5 is 25. Therefore x is 5. That also means that the scale factor of the smallest triangle to the biggest triangle is 5. Thus, x is 5.