Not enough Information. I could say 50 and it would work. I could say 68 and it would work. Any even number thats under 80 but higher than what you think her eldest son is.
To find how long it would take him, one has to divide 400 by 160 and then multiply 5 by what that number is. You multiply 5 by the quotient because that is the number that would make it proportional. 400/160 x 5 is 12.5, meaning that the answer is 12.5 minutes, or A.
