We see that since they are congruent triangles, their corresponding sides are also equal.
-> 2x + 1 = x + 3.
-> x + y = 3x - 3y
From the first equation, we can solve for x ;
2x + 1 = x + 3
Minus both sides by 1 :
2x = x + 2
Finally, minus both sides by x :
x = 2.
We substitute the value of x = 2 into the second equation :
2 + y = 6 - 3y
Add both sides by 3y :
2 + 4y = 6
Solve for y : 4y = 4 -> y = 1.