To solve the equation \( 8 + 4r = 9r + r - 10 \), we can first simplify the right side of the equation:
\[ 9r + r = 10r \]
Now, the equation becomes:
\[ 8 + 4r = 10r - 10 \]
Next, we'll rearrange the equation to get all terms involving \( r \) on one side and constant terms on the other side. Subtract \( 4r \) from both sides:
\[ 8 = 10r - 4r - 10 \]
This simplifies to:
\[ 8 = 6r - 10 \]
Now, add 10 to both sides:
\[ 8 + 10 = 6r \]
This gives us:
\[ 18 = 6r \]
Next, divide both sides by 6:
\[ r = \frac{18}{6} = 3 \]
Thus, the solution is:
\[ \boxed{3} \]