What is the missing value in the equation

2 3/12+3/? = 2 5/8

2 3/12 + 3/x = 2 5/8

simplify to

9x+12/4x = 21/8

Cross multiply

(9x+12) / (4x) = 21/8

(9x+12) * (8) = 21*4x

72x+96 = 84x

Subtract 84 x from both side

72x+96 - 84x = 84x - 84x

-12x+96 = 0

Subtract 96 from both sides

-12x+96-96 = 0-96

-12x = - 96

Divide both sides by 12

-12x/-12 = - 96/-12

x = 8

The missing value is 8