Question

question no 8 pls explain this to me​

Answer 1

$5(y - 1) + 3(2y - 5) + 9y = 180 \\ 20y - 20 = 180 \\ 20y = 200 \\ y = 10degree \\ so \: it \: is \: acute \: angle$
and it is a right angle triangle

Answer 2

sum of all angles of a triangle is 180

5(y-1) + 3(2y-5) + 9y = 180

(5y-5) + (6y-15) + 9y =180

5y + 6y + 9y - 5 - 15 =180

20y - 20 =180

20y =180+ 20

20y = 200

y = 10

angle 1st = 44'

angle 2nd = 45'

angle 3rd =90'