To determine how many sweatshirts were sold, we first need to understand the pricing due to the sale.
Let’s denote the price of the first sweatshirt as \( P \) and the price of the second sweatshirt (at 30% off) as:
\[ 0.7P = 28 \]
From this equation, we can solve for \( P \):
\[ P = \frac{28}{0.7} = 40 \]
Thus, the price of the first sweatshirt is $40, and the price of the second sweatshirt is $28.
Now, when customers buy one sweatshirt and get the second one at 30% off, the total cost for one pair of sweatshirts is:
\[ P + 0.7P = 40 + 28 = 68 \]
Now we can find out how many pairs of sweatshirts were sold to reach the total sales of $748:
\[ \text{Number of pairs} = \frac{748}{68} \approx 11 \]
This means 11 pairs were sold, which corresponds to:
\[ \text{Total sweatshirts sold} = 11 \times 2 = 22 \]
Therefore, the total number of sweatshirts sold in the first hour is:
\[ \boxed{22} \]