Find the value of x in each triangle

The answer for number 1 is 48. the answer for number four is 90. you get your answer by adding the two degrees and subtracting it from 180.

Triangles' angles add up to 180 degrees, since a square has 360 and a triangle is half a square,
For the top one, 90+42+x=180, 90+42=132, 180-132=48, x=48
For the bottom one, 61+29+x=180, 61+29=90, 180-90=90, x=90