Hi Carol,

The technique here is to first decide which of the unknown quantities you and to designate by a letter. Here the important unknown quantities are the number of women and women who where on the train in Erie. Thus I would let $W$ be the number of women on the train in Erie and $M$ be the number of men on the train in Erie.

A train leaves Erie with twice as many women as men.

Said in terms of $W$ and $M$ that is

\[W = 2 \times M.\]

At York, 17 men get on and 16 women get on

In terms of $W$ how many women are on the train now? In terms of $M$ how many men are in the train now? There are the same number so know you have a second equation in $W$ and $M.$ Solve for $W$ and $M.$

Make sure you verify your answer.
Penny