Question

I need help :((((((((

Answer 1

An equation has an infinite number of solutions if the left and right sides are identical. Let's simplify them both and then decide the value of ?.

Left hand side:

$5(x-4)+? = 5x - 20 + ?$

Right hand side:

$1+12x-21 = 12x-20$

So, both sides have a numeric part of -20. We can use the "?" value to make sure that the literal part is the same as well. So, we want

$5x+? = 12x \iff ? = 12x-5x = 7x$