The measures for the given angles B and E are 12° .
Triangles are similar when the correspondent angles and the ratio of correspondent sides are equal. Also, it must present the same shape, but it is not mandatory the same dimension.
Like the triangles are similar, ∠B=∠E. Then,
∠B=∠E
3y=6y-12
3y-6y=-12
-3y=-12
y=4
You can write too:
AC=DF
7a+5=5a+9
7a-5a=9-5
2a=4
a=2
Therefore,
∠B=3y= 3* 4 =12
m∠E=6y-12=6*4-12=21-12=12
AC=7a+5= 7*2+5=14+5=19
DF=5a+9=5*2+9=10+9=19
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