first, we look at the non-fractional numbers:

8-4 = 4

then we examine the fractional portions:

7/12 < 7/8 > 4/10

7/12 < 4/10

we note that larger fractions are being subtracted from the smallest fraction, so the fractional portion becomes negative and the final answer will be less than 4

we make a quick coarse estimate of something a bit greater than '3'