Tween width not working correctly

I’m seeing other people are experiencing some problems with tween, but I report it here anyway.
I want to tween the width of a sprite by using
PlayerShip.FireBullet::ShotsBeforeNextReload()/PlayerShip.FireBullet::MaxAmmo()*292
It returns NaN and doesnt work directly.

When I first store it in a variable, and then use the variable for the width of the tween, then it works.