Hi Can anyone help – equations are new to me and I am trying to get to grips with them. Doing Q3 in June 2010 exam part C where it asks if demand for W fell by 200 W = 00 and 2w + 2L = 1200 by substitution L = 400 however when I checked to see if it would work with the other equation (as I did with the others – and they did) 200W 7W + 5L = 3500, by substition L then = 420 – why is that? I am very confused – can you not always use either equation for substitution?