Tìm x, biết: 390 :(5x -5) =39

a.390 : (5 x X - 5) = 39

b,X x 13 - X x 10 = 240

c,(10 - 5 x X) x (8 x X - 56) = 0

d,280 + 3 x X + 2 x X = 300

e,25 x (2 x X - 4) x 12 = 0