Let's simplify the expression step by step:

First, simplify the expression within the parentheses:
7 x - x = 6 x
7y(6 x) = 42xy

Next, simplify the expression x(x-y):
x(x-y) = x^2 - xy

Then, simplify -7xy(7x-y):
-7xy(7x-y) = -49x^2y + 7xy^2

Now, put all the simplified expressions together:
42xy + x^2 - xy - 49x^2y + 7xy^2 + 7x - y

Combine like terms:
x^2 + 42xy - 49x^2y - xy + 7xy^2 + 7x - y

Therefore, the simplified expression is:
x^2 - 7x - 48xy - 49x^2y + 7xy^2 - y