To solve this equation, we need to combine like terms and isolate the variable y on one side of the equation.

Given equation: 3y + 16 + 4 - 1 + 5y - 10 = 21

Combining like terms, we get: 8y + 9 = 21

Next, subtract 9 from both sides of the equation to isolate the variable:

8y + 9 - 9 = 21 - 9
8y = 12

Now, divide by 8 to solve for y:

8y/8 = 12/8
y = 1.5

Therefore, the solution to the equation is y = 1.5.