To solve this, we need to write a system of equations.
We know that it took her 62 minutes to assemble 11 small and 1 large.
Let's call the small arrangements S, and the large L.
Then:
After lunch, she did 12 small and 1 large in 67 minutes. Then:
Now we have the system of equations:
To solve by elimination, we need to eliminate one unknown by adding or substracting the two equations. If we rest the first equation to the second equation:
Now we can solve:
To make a small arrangement takes her 5 minutes. Now we can go back to the first equation and replace S = 5:
And solve for L:
Then it takes her 7 minutes to make a large arrangement.