a. angles of a triangle add up to 180 degrees.
70 + 50 + x = 180
120 + x = 180
x = 60 degrees
b. Using the same logic, and remembering a right angle = 90 degrees, 40 + 90 + x = 180
130 + x = 180
x = 50 degrees
c. First you need to find angle x. When two lines intersect like in picture c, the two angles across from each other are equal to each other, so x = 60 degrees
Now that you know 2/3 of the triangles angles, you can find y.
75+60+y=180
135+y=180
y=45 degrees
d. A straight line equals 180 degrees. Angle y and the 110 degree angle make up a straight line, so y + 110 = 180. y = 70 degrees
Now you have 2/3 angles of your triangle
70 + 65 + x = 180
135 + x = 180
x = 45 degrees