Are these pairs of shapes enlarged or reduced? Write down the factor of enlargement or reduction in each case.

The smaller square has side lengths of 2 units by 2 units.

The larger square has side lengths of 4 units by 4 units.

Since the larger square's side length (4 units) is twice the smaller square's side length (2 units), the shape has been enlarged.
The factor of enlargement is $\frac{4}{2} = 2$.

a) $\boxed{\text{Enlarged by a factor of 2}}$

b)

The larger rectangle has side lengths of 4 units by 7 units.

The smaller rectangle has side lengths of 2 units by 3.5 units.

Since the smaller rectangle's side lengths (2 units and 3.5 units) are half of the larger rectangle's side lengths (4 units and 7 units), the shape has been reduced.
The factor of reduction is $\frac{2}{4} = \frac{1}{2}$ or $\frac{3.5}{7} = \frac{1}{2}$.

b) $\boxed{\text{Reduced by a factor of } \frac{1}{2}}$