HOW DO YOU KNOW WHEN AN EQUATION HAS INFINITELY MANY SOLUTIONS AND WHEN AN EQUATION HAS NO SOLUTION??

If after you have followed all the correct steps of solving the equation, the variable terms have all dropped off, look at the final statement.

if the statement is true, e.g. 2 = 2, then there is an infinite number of solutions.
If the statement is false , e.g. 4 = 0, then there is no solution.