Well from the equation $45.50 represents y (in this case) and now you're finding x.
     y = 7x
      45.50 = 7x   Divide both sides of the equation by 7 to find x.
     45.50/7 = 7x/7
     6.50 = x
Hence she worked 6.5 hours (or 6 hours 30 minutes.)
HELPFUL?