Ms. Maryna has 10 lbs of 25% sugar syrup. How much sugar does she need to add to make 40% sugar syrup?

You could do 10 x

25 = 40

if you cross multiply its 10 times 40 which is 400, and 25 times x which is 25x, u need to isolate the variable so what you do on one side you do to the other, since you have to do 25x divided by 25 to isolate the variable, you do 400 divided by 24 getting u an answer of 16