Tìm x biết 1/3x4 + 1/4x5 + . . . + 1/14x15 = x/30

Tìm x biết :
a ) 1/3x4 + 1/4x5 + . . . + 1/14 x 15 = x/30
b ) ( 1/2 + 1/4 + 1/8 + 1/6 ) : x = 1/2 + 1/6 + 1/12 + 1/20 + . . . + 1/32