Question

is the given number a solution of the equation? c = 2c – 4; 8

Answer 1

Try it.
8 =? 2*8 - 4
8 =? 16 - 4
8 =? 12

8 is not a solution of the original equation

Try 4
4 = 2*4 - 4
4 = 8 - 4
4 = 4 and yes 4 works.

4 is unique. No other solution will work.