Did you use your scale that 1/4 inch equals 40 feet?.
b1: How many 1/2 inches are in 3.5 inches?. 7
b2: How many half inches are in 5 inches?. 10
Proceed in that fashion and you should be OK. It's like that other problem I stepped through involving scales.
Find the square feet form this and then divide by 43,560 to find the acres.