∠1∠1 and ​ ∠2∠2 ​ are a linear pair, and ​ ∠2∠2 ​ and ​ ∠3∠3 ​ are vertical angles. m∠2=(5+4y)∘m∠2=(5+4y)∘ and ​ m∠3=(6y−25)∘m∠3=(6y−25)∘ . What is m∠1m∠1 ?

Linear pair of angles ads up to 180°. Vertical angles have same value.
According to this we have:
m<1 + m<2 = 180°
m<2=m<3

We can use this to solve for m<1.
m<2=m<3
5+4y=6y-25
4y-6y=-25-5
-2y=-30
y=15
m<2=5+4*15
m<2=65°

m<1 + m<2 = 180°
m<1 + 65° = 180°
m<1 = 180° - 65°
m<1 = 115°