Tìm a biết: a) a : 6 = 71 b) 456 – a = 78 : 3

a) a : 6 = 71
    a      = 71 ´ 6
    a      = 426b) 456 – a = 78 : 3
    456 – a = 26
              a = 456 – 26
              a = 430