Ineed to know how i go about to solve this question

You should probably start by changing the fractions into decimals. then you multiply the decimal of 1 1/4 by the decimal of 3 1/2. Next you multiply the decimal of 1 3/4  by the decimal of 3 1/2. then you find the difference and that's your answer, alternatively you could leave them as fractions, do the same thing and then change it into a decimal. 
Hope this helps :) 

The answer is b: step 2.