If the length of the first rectangle divided by the length of the second rectangle is the same as the width of the first rectangle divided by the width of the second rectangle, then both rectanges are similar.
Top left one: 50/10 = 5. 30/6 = 5. They equal so that is one of the answers.
Top right one: 5.2/2.6 = 2. 3.8/1.2 = 3.16666... Not one of the answers.
Bottom left one: 100/10 = 10. 49/7 = 7. Not one of the answers.
Bottom right one: 7.5/2.5 = 3. 4.5/1.5 = 3. They equal So that is one of the answers.
So the only anwers are the top left one and the bottom right one.