What Is the perimeter if a rectangle if the area is 45cm2?

Any number greater than or equal to 4*sqrt(45) cm or 26.83 cm (approx).

To see that, suppose L ≥ sqrt(45) cm be the length of the rectangle

and let B = 45/L cm

Then Area = L*B = L*(45/L) = 45 cm2

If L = 9cm, then B = 45/9 = 5 cm and then perimeter = 2*(L+B) = 28 cm

If L = 90 cm, then B = 0.5 cm and P = 181 cm

If L = 900 cm, then B = 0.05 cm and P = 1800.1 cm

If L = 9000000 cm then B = 0.000005 cm and P = 18000000.00001 cm

As can be seen, the perimeter can be increased without limit.