15. Rezolvați ecuațiile in R:
a) 3(2x + 1) + 4(2x - 1) = 2(3x + 4)+7
b) 2(2x + 1) - 4(x + 3) = 5 - 3(2x + 3);
c) 3(2x - 7) - 5(3x + 1) + 4x =8 - 2(5x - 3);​