RS + ST = RT
a.
2x + 10 + x - 4 = 21
3x + 6 = 21
3x = 21 - 6
3x = 15
x = 15/3
x = 5
RS = 2x + 10 = 2*5 + 10 = 10 + 10 = 20
ST = x - 4 = 5 - 4 = 1
b.
3x - 16 + 4x - 8 = 60
7x - 24 = 60
7x = 60 + 24
7x = 84
x = 84/7
x = 12
RS = 3x - 16 = 3*12 - 16 = 36 - 16 = 20
ST = 4x - 8 = 4*12 - 8 = 48 - 8 = 40
c.
2x - 8 + 11 = x + 10
2x + 3 = x + 10
2x - x = 10 - 3
x = 7
RS = 2x - 8 = 2*7 - 8 = 14 - 8 = 6
RT = x + 10 = 7 + 10 = 17
d.
4x - 9 + 19 = 8x - 14
4x + 10 = 8x - 14
10 + 14 = 8x - 4x
24 = 4x
x = 24/4
x = 6
RS = 4x - 9 = 4*6 - 9 = 24 - 9 = 15
RT = 8x - 14 = 8*6 - 14 = 34