Find the missing number so that the equation has infinitely many solutions.–3x–20=–3x+

The missing number in the equation is 20.

Here's the step by step solution:

The equation is -3x - 20 = -3x + __

For an equation to have infinitely many solutions, both sides of the equation must be identical. That means whatever is added or subtracted on one side must be the same on the other side.

In this case, we have -3x - 20 on the left side and -3x + __ on the right side.

To make both sides of the equation identical, the blank must be filled with -20.

So, the equation becomes -3x - 20 = -3x - 20, which has infinitely many solutions because any value of x will satisfy this equation.