Please help me in this small question.

y = 80

Step-by-step explanation:

The sum of the interior angles of a polygon is

sum = 180° (n - 2) ← n is the number of sides

Here n = 5 , thus

sum = 180° × 3 = 540°

Sum the internal angles and equate to 540

110 + y + 2y + y + 110 = 540 , that is

4y + 220 = 540 ( subtract 220 from both sides )

4y = 320 ( divide both sides by 4 )

y = 80

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.