To answer this equation you have to find a number that fits the description of what is required. It may seem difficult but it's not first off it's trial and error you have to find the right equation for every given number. For example, what makes 15 equal 5 true? To make the equation true you have to do 15 divided by 3 equals 5 now we take the / 3 and apply them to all the other numbers so 21 / 3 is 7 , 36 divided by 3 is 12 hi, 60 / 3 is 20 , 90 /3 is 30. If you have any other question like this all you have to do is trial and error with a number to make the equation true hopefully that helps! (B.t.w / symbol means divided by)
