Question

let y=21 and x=1.5 if y varies directly with x find y when x=9

Answer 1

If $y$ varies directly with $x$ then we have the following function:
$y=x + (21 - 1.5)$ or simply $y = x + 19.5$.
So, when $x=9$:
$y = 9 + 19.5 = 28.5$

Answer 2

Y would be 42. if you multiple 1.5 by 3 it will be 9. so if divide 21 by 1.5 it equals 14 so multiple 14 by 3 it gives you 42