21+124569:9-2×a= 6737+107
124569:9-2×a = 6844-21
13841-2×a = 6823
2×a = 13841-6823
2×a = 7018 |:2
a = 3509
(18×b-1278):149 = 36
18×b-1278 = 36×149
18×b = 5364+1278
18× b = 6642 |:18
b = 369
[(c+41+56):2-20]:10 =3
(c+97):2-20 = 3×10
(c+97):2 = 30+20
c+97 = 50×2
c+97 = 100
c = 100-97
c = 3
