when you multiply fractions, all you need to do is multiply the numerators by themselves, and the denominators by themselves. so all you need to do is multiply 4•3 (12) and 9•4 (36) so your new fraction is 12/36. to simplify this fraction, 12 happens to go into 36 3 times. so the simplified fraction would be 1/3. for the whole number, multiply 9•9 (81) and then you have your exact answer, 81 1/3.
to estimate, the first fraction is less than one half, so you should round down to 9. the second number is more than one half so you should round up to 10. 10•9= 90. the estimate is 90
