How can i use models to add fractions?

It can show how much you have and how much you want

First, we put the measurements in a ratio.
Then, we cross multiply so that 15 and 41 are multiplied together and 20 is multiplied by (x+9)
We then expand 20*(x+9), so that it becomes 20x+180= 15*41
Which is 20x+180= 615
We tune solve the equation for x, which is 21.75
But we aren't done yet because the ratio is x+9:41
We have x but we have to plus it with nine to get the final answer
So, our answer is 30.75
Hope this helps :)