The answer is: 12 centimeters.
The explanation is shown below:
1. By definition, all four sides of the square are equal and the diagonals are equal too.
2. Keeping the information above on mind, you know that AC and BD are equal:

3. Then, the length of BD is twice BE. So, you can calculate it as following:


4. Therefore, the lenght of AC is:

3m + 2n= p solve for n
subtract 3m on both sides
2n = p - 3m
divide both sides by 2
n = p/2 - 3m/2
-----------------------
xy - 5 = k solve for x
add 5 on both sides
xy = k + 5
divide both sides by y
x = k/y - 5/y
$260.00
Because you won’t need to multiply the $60.00 per person
Not is posible because no exist a igualty