But I Have To Know The Answer First!

Consider statement 1 :

$\text{The digits used in the next sentence are all equal.}$

So we know that both the blanks must be filled with the same digit (digits from $1$ to $9$ inclusive).

Consider statement 2 :

$\text{The number of times the digit} \text{\_\_\_\_\_} \text{is used in this sentence is} \text{\_\_\_\_\_}.$

Now, whatever the digit we use to fill one of the blanks will be same digit that is to be filled in the other blank (condition from statement 1 ).

Also, the number of times we use the digit will be the equal to the number of blanks we put it in (condition from statement 2 ). Further we can deduce that the digit to be used is equal to the number of blanks it has to be filled in .

$\therefore$ The digit that satisfies the criteria is $2$ .

And sum of the missing digits: $2+2=\boxed{4}$ .