You have to multiply the numerator (top) and denominator (bottom) by a number that would make the bottom number the same for both fractions (common denominator). So for 3/4, you can multiply each number by 3 to get the common denominator 12. So 3*3=9, and 4*4=12. For 2/6, we can multiply by 2 to get 12 for the denominator. 2*2=4, and 6*2=12.
