Fraction1: 3/4
Fraction2: 5/6
The common denominator is found by multiplying both denominators together.
4 * 6 = 24 = your new common denominator.
If you want to make the new fractions, you have to have the respective numerator. this mean you must do what you did to the denominator to the numerator. In this case we multiplied the denominator of the 3/4 by 6 so we also have to multiply the numerator by 6.
New Fraction1 would be:
18/24
Do the same thing with Fraction2 only multiply the fraction 5/6's numerator by 4
New Fraction2 would be:
20/24
Hope this helped.