Having an issue creating this in C-Sharp C#

Cant seem to fifure out how to do math in an array

After catching the returned cost Array, create one last custom function called SumOfCosts.

a. This array should accept the cost array as a parameter.

b. Inside of this function create a variable to hold the total sum of the items costs.

c. Loop through each item in the cost Array and add their total to the sum.

d. Return this sum to the Main method. Use the total sum variable that is return in a final output to the user that is in this format.