Answer:
There were 360 boxes before addition.
Explanation:
Let the number of stacks be 'x'.
Given:
Number of boxes in each stack = 12 boxes.
So Total number of boxes will be equal to number of boxes in each stack multiplied by Number of boxes in a stack.
framing in equation form we get;
Total number of boxes =

Also Given:
Additional boxes arrived = 60
So Total number of boxes will be =

Now After addition number of boxes in each stack = 14
Now Total number of boxes after addition will be equal to number of boxes after addition in each stack multiplied by number of stacks.
framing in equation form we get;

Combining like terms we get;

Now Dividing both side by 2 we get;

Now Number of boxes before addition =

Hence there were 360 boxes before addition.