Hello!
First, let's rewrite some important information contained in the exercise:
• 14 blue pens.
,• 8 black pens.
,• 6 red pens.
• Total: 28 pens.
Well, let's think for a moment:
If he won't pick up either black or red pens, it means he can only pick up blue pens, right?
So, we can write it as a fraction, decimal or percent:
[tex]\frac{\text{ number of blue pens}}{\text{ total of pens}}=\frac{14}{28}=\frac{1}{2}=0.5=50\%[/tex]