Question

What is AB?

Answer 1

I am not sure about the `m < A` bit...but anyway...

Explanation:

I think that the questions tells us that the angle in `A` is `60^@` so that using trigonometry:
`bar(AC)=bar(AB)cosÂ`
where `Â=60^@` is the angle in `A`
and
`bar(AC)=68cm`
rearranging:
`bar(AB)=68/cos(60^@)=68/(1/2)=136cm`