Answer:
x = x; the solution has infinite solutions
Explanation:
3(x+ 7) = 3x + 21; distribute the 3 on the left side
3x + 21 = 3x + 21; now subtract 21 from both sides
3x = 3x; divide by 3
x = x; the solution has infinite solutions. Since both terms are equal any value for x will be true on this equation.