Answer:
x = 0 or x = -3/7
Explanation:
The equation is a second order polynnomial and would therefore have two solutions for x.
The solution of the set can be expressed as:

The x is a common term in the expression so we can write is as:

Where the expression is equal to zero the first solution of x is 0: x=0
The second part (7x+3) is also equal to zero and therefore:

After simplification x = -3/7
The solution of the set is x=0 or x=-3/7
Substituting either in the left hand side of the equation will make the whole equation equal to zero.