Hey there! I'm happy to help!
If Mary's friend at 3/4 of blackberries, we will simply multiply the total number of blackberries by 3/4 to find how many blackberries Mary ate.
3/4×1 3/4= 1 5/16
Therefore, Mary's friend at 1 5/16 pounds of blackberries.
I hope that this helps! Have a wonderful day!