Its 37 and yea its an easy question lol
Answer:
A. Stone bridges to steel bridges=
12 : 20
6 : 10
3 : 5
answer = 3 : 5
B. Steel bridges to Stone bridges
20 : 12
10 : 6
5 : 3
answer = 5 : 3
Total bridges = 20+12=32
C. Total bridges to steel bridges
32 : 20
16 : 10
8 : 5
answer = 8 : 5
I m getting 308.11, there is an additional 0.60 that is added, maybe your source is wrong, or there is a copying error.