Answer:
x=5
Step-by-step explanation:
We know that corresponding sides will have the same angles. In this case it's 12 and 12+3=15. That means that larger triangle is 15/12=5/4=1.25 times larger.
So we apply that for 3x+1 as well.
1.25(3x+1)=4x
3.75x+1.25=4x
.25x=1.25
x=5
