Abaking tray is 700mm by 500mm.
a cake tin is 25cm in diameter.
how many cake tins can fit on the tray at one time.

So first find the area of the baking tray then the area of the cake
area of tray=legnt times width=700 times 500=350,000 mm

area of cake, assuming cake=circle
area of circle=pi times radius^2
2 times radius=diameter
radius=diameter/2
radius=25/2
radius=12.5
pi times r^2=pi times 12.5^2=490.874 cm^2

PAY ATTENTION TO UNITS

so
1 cm=10 mm
350,000 mm=35,000 cm

so
tray=35,000 cm^2
cake=490.87
how many cakes per tray
area:
cake times x=tray
divide by kake
x=tray/kake=35000/490.87=71.3
your teacher probaly wants whole cakes to fit on the tray since you don't really want to fit 0.3 cake on a tray so round and get 71 kakes

answer is 71 cakes