Rectangle 1: 1/3 shaded
Rectangle 2: 1/4 shaded
First you have to look through each denominators multiples to find the lowest common denominator (LCD).
Multiples of 3: 3, 6, 9, 12, 15
Multiples of 4: 4, 8, 12, 16, 20
As you can see, both numbers are multiples of 12.
Rectangle 1: 1/3 shaded= 4/12 shaded
Rectangle 2: 1/4 shaded= 3/12 shaded
I made equivalent fractions by multiplying both the numerator and the denominator by the same number.
The least number of parts which both rectangles can be divided is 12.
Hope this helped :)