Step 1: Radius of the circular sheet, $r=70$ cm.
Step 2: Area of the full circular sheet
$$=\pi r^{2}=\frac{22}{7}\times 70\times 70=15400\text{ cm}^{2}$$
Step 3: A quadrant is one-fourth of the circle, so the remaining part is three-fourths of the circle.
Step 4: Area of the remaining sheet
$$=\frac{3}{4}\times 15400=11550\text{ cm}^{2}$$
Hence the area of the remaining sheet is $11550$ cm$^{2}$.