Answer:
x=7.2
Step-by-step explanation:
Since these two triangles are very similar to each other, let's make this easy on us and mentally flip the smaller triangle.
Now, since the angles are the same we can use ratios to figure out x.
Since the sides 5 and 3 are on the same side, we can find a multiplier that leads 5 to 3.
3/5=0.6
So, the triangle's sides get decreased 0.6 times the original values.
Multiply 12*0.6 to get value x and we get 7.2
