Add 3√21 + 7√21 (1point)

To add 3√21 + 7√21, we can combine like terms. Since both terms have the same radical (√21), we can simply add their coefficients:

3√21 + 7√21 = (3 + 7)√21 = 10√21

So, 3√21 + 7√21 = 10√21.