When two triangles are similar, then the ratios of their corresponding sides will be equal:
so 2.4/3 = 2.8/x = y/4.5
Use the ratio that involves the x and the two values that are given:
2.4/3 = 2.8/x
Then, solve the equation for x to find the missing side:
2.4/3 = 2.8/x
(2.4 / 3 ) x = 2.8
x = 2.8 / (2.4/3)
x = 3.5
The correct option is A.