Question 443598
Our current probability is 5 reds / (5+6+3+2) crayons 

or  5/16 .

Let x be the number of crayons needed to be added.

Then, {{{(5+x)/(16+x) = 2/3}}}
cross-multiply to get:

{{{3(5+x) = 2(16+x)}}}
{{{15+3x = 32 + 2x}}}
{{{highlight(x = 17)}}}