Recall the formula for weight.

Weight ($W$) is the product of mass ($m$) and acceleration due to gravity ($g$).

$$W = mg$$

To find mass, divide weight by acceleration due to gravity.

$$m = \frac{W}{g}$$

Given $W = 45.4\,\text{N}$ and $g = 10\,\text{m/s}^2$.

$$m = \frac{45.4\,\text{N}}{10\,\text{m/s}^2}$$ $$m = \boxed{\text{4.54}\,\text{kg}}$$

3b) Find the weight of a box of mass $50\,\text{kg}$ and $g = 10\,\text{m/s}^2$.

Weight ($W$) is the product of mass ($m$) and acceleration due to gravity ($g$).

$$W = mg$$

Given $m = 50\,\text{kg}$ and $g = 10\,\text{m/s}^2$.

$$W = 50\,\text{kg} \times 10\,\text{m/s}^2$$ $$W = \boxed{\text{500}\,\text{N}}$$