To find the total number of pages printed, we need to consider the number of pages in each type of packet and how many of each type are printed:
- Each 6th-grade packet has 10 pages and there are \( p \) 6th-grade packets, resulting in \( 10p \) pages.
- Each 7th-grade packet has 12 pages and there are \( r \) 7th-grade packets, resulting in \( 12r \) pages.
To get the total number of pages printed, we add the pages from both types of packets:
\[ \text{Total pages} = 10p + 12r \]
Thus, the expression that represents the total number of pages printed is \( 10p + 12r \).
If this expression corresponds to one of the options A, B, C, or D, you would need to check against those options to identify the correct one. However, based on the information provided, the correct expression is \( 10p + 12r \).