8х-9x=3x+16

Let's solve the equation \( 8x - 9x = 3x + 16 \).

First, simplify the left side:

\[ 8x - 9x = -1x \]

So the equation becomes:

\[ -1x = 3x + 16 \]

Next, add \( 1x \) to both sides:

\[ 0 = 4x + 16 \]

Now, subtract 16 from both sides:

\[ -16 = 4x \]

Now, divide both sides by 4:

\[ x = -4 \]

So the solution to the equation is

\[ \boxed{-4} \]