Hello!
The answer is:
She will need 9 tins to cover all the panels.
Why?
To find how many tins will she need to cover the 30 panels for her allotment and her garden, we need to calculate the total area of the panels and then, calculate how many tins will she need knowing that each liter of tin, covers 12 square meters.
We are given the dimensions of the panels:

Now, calculating the area of one (1) panel, we have:

So , the total area of all 30 panels is:

Then, calculating how many tins will she need to paint all the panels, we have:

Hence, we have that she will need 9 tins to cover all the panels.
Have a nice day!