2*3/4 says 2 times 3 quarters. 2*3=6 (of anything) so we have 6 quarters or 6/4. 2 divides top and bottom so we have 3/2, or 3 halves. That's 1½.
Another way: in US a quarter is a 25-cent piece. Get 6 quarters. 4 of them make $1 and two make a half dollar. So we have $1 and a half or $1.50. Or put the quarters together in twos: 3 half dollars.