Tìm x, biết:
a, 390 – (x – 7) = 169:13
b, (x – 140) : 7 = 33-23.3
c, x – 6 : 2 – (48 – 24) : 2 :6 – 3 = 0
d, x + 5.2 – (32+16.3:6 – 15) = 0
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