Respuesta :

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The angles are complementary so their angles measures add to 90 degrees.
4y + 7 + 3y - 1 = 90
7y + 6 = 90
subtract 6 from both sides
7y = 84
divide both sides by 7
y = 12

4(12) + 7 = 55 degrees
3(12) -1 = 35 degrees
The diagram shows it is a right angled triangle so you know that:

4y + 7 + 3y - 1 = 90

Which you can simplify to

7y + 6 = 90

And

7y = 84

Therefore if you divide both sides by 7 you get

Y = 12