3/7 by 9/10 =
(3/7) * (9/10) = 27/70
4/9 by -3 =
(4/9) * (-3) = -12/9 = -4/3
To multiply fractions, you need to multiply the numerators (the top part of the fraction) together and multiply the denominators (the bottom part of the fraction) together.
In this case, to multiply 3/7 by 9/10:
Multiply the numerators: 3 * 9 = 27
Multiply the denominators: 7 * 10 = 70
The result is 27/70.