13 + x = 78

13 + x – 13 = 78 – 13

x = 65

x + 7 = 49 · 2

x + 7 = 98

x + 7 – 7 = 98 – 7

x = 91

25 + y = 105 – 5

25 + y = 100

25 + y – 25 = 100 – 25

y = 75

a – 197 = 103

a – 197 + 197 = 103 + 197

a = 300

b – 78 = 17

b – 78 + 78 = 17 + 78

b = 95

(x – 8) – 21 = 14

x – 8 – 21 = 14

x – 29 = 14

x – 29 + 29 = 14 + 29

x = 43