You've got the right equation, which is always a good start :) If you're not sure what to do next then the best thing to do is write down everything you know. Let's try that. First, the thing we want to know is the distance from house to metro, we'll call this .

The first useful piece of information is that work is 33 miles away, from this we know that plus the distance from metro to work is 33. Or as an equation:

Next we are told about the travel speeds, from which we can work out the travel times. She rides the bike at 7 mph so . Similarly she rides the metro at 39 mph so

Finally we know the difference between the times is 0.35, so . If you look back on what we've done, you should notice we have four equations, and four variables, which is solvable. Hopefully you can do the rest now.

I think the answer comes out at a little above 7. If you have any problems or didn't follow what I did then plaese write back.

Hope that helps.

Kev