[Please Help]

Hello all,

I have 3 tables in my Word file. In Table 3, there is only one row with one
cell, and in that cell, I want to have a formula to add the numbers from C5
and C7 in Table 1 and Table 2, respectively. I tried the formula
{=sum(Table1 C5 + Table 2 C7)} in the cell in Table 3.

Prior to inserting that formula, I created the bookmarks "Table1" and
"Table2" by highlighting respective table and go to InsertBookmark.

I am completely new to the writing a formula in Word and creating a
bookmark. Please help with detail steps.

Thanks.