Answer:
70
Step-by-step explanation:
91 ÷ 1.3 = 70
There chance for just getting across each row would be 50% but there chance of getting across completely is 1 in 18
I am not sure on how to do this however here is a link with information thst will be able to help you around this subject.i hope this helps
https://www.bbc.com/bitesize/guides/z8k887h/revision/1