To solve this problem, we must first simplify the expression (2/5 - 7/10) as follows:

2/5 - 7/10 = (4/10) - (7/10) = -3/10

Now, we can add this result to 1/4 + 2,1:

-3/10 + 1/4 + 2,1 = -3/10 + 1/4 + 21 = -3/10 + 1/4 + 21
= -3/10 + 1/4 + 21
= -6/20 + 5/20 + 84/20
= (-6 + 5 + 84)/20
= 83/20

Therefore, 1/4 + 2,1 is equal to 83/20.