Hi there! I'm kind of confused about how to solve this!

Each ladder had 30 rungs.
Bob went down two rungs every second.
Roy went up one rung every second.
At some point, Bob and Roy were at the same height. Which rung were they on?

The answer is the 10th rung, but do I solve this using equal values, substitution, or the elimination method?

1- is the product of two rational numbers irrational or rational? first, make a hypothesis by multiplying two rational numbers. then, use variables such as x=a/b and y=c/d and the closure property of integers to prove your hypothesis. 2- what do you think the product of a nonzero rational number and an irrational number is? is it rational or irrational? make use of variables, the closure property of integers, and possibly a proof by contradiction to prove your hypothesis. 3- why do we have to specify that the rational number must be nonzero when we determine what the product of a nonzero rational number and an irrational number is? if the rational number were 0, would it give us the same result we found in part b?