so assuming that 25cm is 25 square cm because you cannot have a 2 dimentional cake so
600mm by 500mm
to find the area, multiply legnth by width
mm=milimeters
cm=centimeters
this is in mm so
1cm=10mm
1mm=1/10cm
to convert from mm to cm, you divide by 10
we must divide by 10 first
legnth =600mm
600/10=60cm
legnth=60cm
width=500mm
500/10=50cm
width=50cm
area=60 times 50=3000 square cm or cm^2
so 3000 is the area
25 is the area of each cake
divide 3000 into 25 and find how many cakes will fit
3000/25=120
120 cakes will fit