Question 4704
Number 1: This is an average problem.  Write in everything you know, substitute a letter for what you don’t know, and then solve for the unknown letter.

{{{(87 + 81 + 88 + x)/4 = 87}}}

Number 2: This is another average problem.  The average, or mean, is the total sum of all your numbers, divided by how many numbers you have.  In this problem, you have 7 numbers.  The sum of these numbers is (8 + 7 + 7 + 5 + 3 + 2+ 2 =) 34.  The average is {{{34/7 = You can solve from here.}}} 

Number 3: This is almost like an average problem.  You still do the same thing.  Write in everything you know, substitute a letter for what you don’t know, and then solve for the unknown letter.
 
For each toy Ben makes, he gets 

$3.00 – $1.80 = $1.20 in profit.   

To earn $36.00 in profit, he has to sell

$1.20 * x = $36.00, where x is the number he has to sell to make $36.00 in profit.