Convert each fraction into an improper fraction: 3&1/2=7/2 and 4&1/2=9/2.
If an improper fraction is represented by a b/c, then the improper fraction is (a*c+b)/c. So 3 1/2 is (3*2+1)/2=7/2.
Then multiply: 7/2 * 9/2 = 63/4, that is 7 times 9=63 divided by 2 times 2=4, to give 63/4. Divide 63 by 4 to get 15 and 3/4.