Question 14133
When you evaluate an expression, just plug in your number for the letter.  My suggestion would be to put parentheses around the number each time you plug it in (it'll help you from getting confused).  When you plug in 3 for a, you will get the equation {{{3(3)(3)+(3(3))(2)}}}.  Use order of operations to solve, which in this problem means that you will do the multiplication before you add.  Here are the steps:

Original Equation:  {{{3(3)(3)+(3(3))(2)}}}
{{{9(3)+(3(3))(2)}}}
{{{27+(3(3))(2)}}}
{{{27+(9)(2)}}}
{{{27+18}}}
=45