The values of y for the missing angles are:
12) y = 5
13) y = 11
15) y = 14
How to find the missing angles?
12) From he given image, we can see that (9x - 2) and (5x + 54) are corresponding angles and as such they are congruent. Thus:
9x - 2 = 5x + 54
9x - 5x = 54 + 2
4x = 56
x = 56/4
x = 14
(10y + 6) is a linear pair with (9x - 2). Thus:
9(14) - 2 + 10y + 6 = 180
130 + 10y = 180
10y = 50
y = 5
13) (8x - 1) and (11x - 25) are alternate exterior angles and as such they are congruent which gives us:
8x - 1 = 11x - 25
11x - 8x = 25 - 1
3x = 24
x = 8
(15y - 48) forms a linear pair with (8x - 1). Thus:
15y - 48 + 8(8) - 1 = 180
15y + 15 = 180
15y = 165
y = 11
15) (12x + 1) and (15x - 26) are corresponding angles and as such they are congruent. Thus:
12x + 1 = 15x - 26
3x = 27
x = 9
Sum of angles in a triangle is 180 degrees. Thus:
12(9) + 1 + 4y - 9 + 28 = 180
4y + 108 + 20 = 180
4y = 56
y = 14