5. Evaluate the following: 1) $$55 \cdot 57$$ 2) $$304$$ 3) $$19 \cdot 21$$ 4) $$748$$. (Some parts are unclear).

Let's evaluate the clear parts:

1. 1) $$55 \cdot 57$$
   We can calculate this as $$(56-1)(56+1) = 56^2 - 1^2 = 3136 - 1 = 3135$$.
   Alternatively, using multiplication:
   

     55
    x 57
   -----
    385 (55 * 7)
   2750 (55 * 50)
   -----
   3135

2. 2) $$304$$
   This appears to be just the number 304, not an operation to evaluate.
3. 3) $$19 \cdot 21$$
   We can calculate this as $$(20-1)(20+1) = 20^2 - 1^2 = 400 - 1 = 399$$.
   Alternatively, using multiplication:
   

     19
    x 21
   -----
     19 (19 * 1)
   380 (19 * 20)
   -----
   399

4. 4) $$748$$
   This appears to be just the number 748, not an operation to evaluate.

Assuming the question intended for calculation where possible:

Ответ: 1) 3135, 2) 304, 3) 399, 4) 748