Given that,

ABCD is a rectangle

CD = 6 cm

AD = 8 cm

We know that,

Area of parallelogram and rectangle on the same base between the same parallels are equal in area

So,

Area of parallelogram CDEF and rectangle ABCD on the same base and between the same parallels, then

We know that,

Area of parallelogram = Base * Height

Area of rectangle ABCD = Area of parallelogram

= AB * AD

= CD * AD (Therefore, AB = CD)

= 6 * 8

= 48 cm²

Hence,

Area of rectangle ABCD is 48 cm²