In this question, you need to convert the height of snow into the height of water. To answer this question, it would be easier to find the ratio of snow: water. If 1.5 feet of snow become 2 inch of water, then the ratio would be 2/1.5= 1 1/3.
Then for 3.5 feet of snow, it would be :
3.5 feet of snow * 1 1/3 inch of water/ feet of snow= 4 2/3 inch of water