We want to know the total of blankets that Greg's collected.
As there are 38 people in the group, and they each gave 2 blankets, they brough a total of 79 blankets.
As they got 29 asking door-to-door, and got another 52, we will sum the values, as shown:

This means that the Greg group collected a total of 160 blankets, instead of 121, and the Greg statement is false.