Is the scientific notation correct or no. please answer this is important

Only A is true

Step-by-step explanation:

I think scientific notation has only one digit at the left of decimal point

Watch carefully . . . this could get really tricky:

-20 = -4x -6x

Do you see the  -4x  and the  -6x  on the right side ?
I'll bet if it said  (4 negative cows)  and  (6 negative cows), you'd know
right away that you could combine them into  (10 negative cows).

-4x - 6x = -10x

So now the equation is    -20 = -10x

Multiply each side by  -1 :  20 = 10x

Divide each side by  10 :    2  =  x

and there you have it.