$$\left(x-2\right)\times 20-x\times 20=\left(x-2\right)\times 4$$
Use the distributive property to multiply $x-2$ by $20$.$$20x-40-x\times 20=\left(x-2\right)\times 4$$
Use the distributive property to multiply $x-2$ by $4$.$$20x-40-x\times 20=4x-8$$
Subtract $4x$ from both sides.$$20x-40-x\times 20-4x=-8$$
Combine $20x$ and $-4x$ to get $16x$.$$16x-40-x\times 20=-8$$
Add $40$ to both sides.$$16x-x\times 20=-8+40$$
Add $-8$ and $40$ to get $32$.$$16x-x\times 20=32$$
Multiply $-1$ and $20$ to get $-20$.$$16x-20x=32$$
Combine $16x$ and $-20x$ to get $-4x$.$$-4x=32$$
Divide both sides by $-4$.$$x=\frac{32}{-4}$$
Divide $32$ by $-4$ to get $-8$.$$x=-8$$