Sheila has 5 times as many markers as Dave. Together, they have 18 markers. How many markers does Sheila have?
Let the number of markers that Dave has = x
So, Sheila has 5 times this number = 5x
And we are told that
x + 5x = 18
6x = 18 divide by 6 on both sides
x = 3
And Sheila has 5x = 5(3) = 15