Please help me solve this

I'm almost too honest to take your points for this.
Almost.


I promise you, you know very well how to do this.
Let's talk about these examples first:

If you have 10 jellybeans, and you give away 4, then how many do you have ?
I hope you said 6 .  That's correct.  How did you figure it out ?  It's easy, right ?  You just subtract (take away) 4 from 10, and you have 6 left.

If you have 8 ounces of soda in a can, and you drink 5 ounces, then how much
is left in the can ?
I hope you said 3 ounces.  How did you figure it out ?
You just subtract (take away) 5 from 8, and you have 3 left.
Easy, right ?

One more quick example:
If you have a string that's 11 inches long, and you cut off 2 inches and
throw it away, then how long is the string that you have left ?
You just subtract (take away) 2 from 11 and you have 9 left.

OK.  Now the real one.  Don't clutch.  Just relax.

If you have a board that's 46 meters long, and you cut off ' u ' meters and
throw it away, how much board do you have left ?
You just subtract (take away) 'u' from 46 and you have (46 - u) left.

That's all there is to it !