If you expand this equation first
You get -4u+6+3u=3u+24
And if you simplify that you get:
-u+6=3u+24
Now you need to solve this equation to find u
First bring 3u to the other side to -u-3u (the positive changes to negative)
Now the equation is
-4u+6= 24
Take 6 of both sides
-4u=24-6= 18
-4u= 18
So u= -18/4
Which simplifies to -9/2
Answer: -9/2