This is because you want to get x alone, so if you divide -12 on one side you have to do it on the other side, so you get -3/-12 which can be divided by -3 to be simplified to 1/4. Hope this helps!
<u></u>You would add 54+42+153=249 to find the total amount of customers from the previous week. Then you would divide 54/249= 0.2168 to find the amount of customers that used cash to total customers. The closest fraction would be about 1/5.
