Answer:
What numbers? Be specific.
Divide the total amount of ribbon by the length of each individual ribbon:
30 ft / 0.625 ft = 48
She can make 48 ribbons.
If the total bill comes to $110.05, we know that we are going to have to take 15% of this for his tip.
So we convert 15% to a decimal by dividing by 100:

Then we multiply this by the amount of the bill:

So if we round this to the nearest cent, we get $16.51.
Therefore, Alberto's tip will be about $16.51.
We need to solve for R, This is really simple.
The original expression is:
R (r1 + r2) = r1r2
To solve for a certain variable, we need to get this variable alone on one side of the equation and equate it with the other side.
In the given expression, to get R alone on one side we have to eliminate (r1 + r2).
In order to do this, we will divide both sides by (r1 + r2).
Doing this, we get the solution as follows:
R = (r1r2) / (r1 + r2)