Can someone me with these and explain step by step? god bless you

I can do 15, 17 and 18. 

15.  (x+5)+4x=180 (A line is 180 degrees.)
you can subtract 5 from 180 to get 175.
 4x+x =175
5x=175
divide 5 to get x=35

plug 35 into x to get 40 and 140.  

17.  Same thing with the line = 180 degrees

6x-4+4x-6=180

10x-10=180
combine like terms.
10x=190
add 10 to both sides
x=19
divide 10.  
plug 19 in 6*19-4=110, so y=110 (since parallel lines)
and 4*19-6=70

19. y=90 (the square means 90 degrees)
 x-7+3x-3=90 (since 90+90=180)
4x-10=90 (combine like terms)
4x=100 (add 10)
x=25
plug it in again to get 25-7=18 and 3*25-3=72

Idon't know the answer