Area of a sector of a circle = (1/2)r²θ,

where r is the radius and,

θ the angle in radians subtended by the arc at the center of the circle

Here, Radius of circle = 28 cm

Angle subtended at the center = 45°

Angle subtended at the center (in radians) = θ 45π/180 = π/4

∴ Area of a sector of a circle =

=

= 308 cm²

Hence, the required area of a sector of a circle is 308 cm^2.