To solve this equation, we first need to find a common denominator for the fractions on the left side of the equation.

The common denominator for 3 and 12 is 12, so we rewrite the equation:

(4y4)/(34) - (5y+4)/12 = -21/8

Now we can simplify the fractions:

(16y / 12) - (5y+4)/12 = -21/8
(4y - 5y - 4) / 12 = -21/8
(-y - 4) / 12 = -21/8

Now we cross multiply to get rid of the fractions:

8(-y - 4) = 12(-21)
-8y - 32 = -252
-8y = -220
y = 27.5

Therefore, the solution to the equation is y = 27.5.