Is there something missing here, this is a linear (1st order problem while

the rest are quadratic (2nd order) problems?

Any way this goes something like:

1. Evaluate the left hand side:

6(80-30) = 6*50 = 300 = 48-x

so we now have:

300 = 48-x

If we subtract 48 from both sides of this equation we still have equality

so:

300 - 48 = 48 - x -48

or:

252 = -x.

Now multiply through by -1 to get:

(-1)*252 = -252 = (-1)(-x) = x,

or:

x = -252.

RonL