Answer
a) $\approx 12.5\;\rm N$
b) $\approx 50\;\rm N$
Work Step by Step
a) We need to estimate the weight of a laptop by using the information given in Table 5.1, as the author told us.
We are given 3 weights of objects in the table, a quarter, a pound, and a person.
The closest weight to our laptop computer is the pound which weighs 5 newtons.
I can guess that my laptop is about 2.5 pounds, so the weight of my laptop is
$$W=2.5\times5=\color{red}{\bf 12.5}\;\rm N$$
b) We need to estimate the propulsion force of a bicycle by using the information given in Table 5.1, as the author told us.
We are given a car's propulsion force, which is about 5000 N.
An average car is about 1000 kg while a bicycle and its rider is about 100 kg, as a rough estimate as well.
Now we can assume that the acceleration of the bicycle is one-tenth that of the car, so the propulsion of the bicycle is given by
$$\dfrac{F_{bicycle}}{F_{car}}=\dfrac{m_{bicycle}a_{bicycle}}{m_{car}a_{car}}=\dfrac{100\cdot 0.1a_{car}}{1000a_{car}}=\dfrac{1}{100}$$
Thus,
$$ {F_{bicycle}} =\dfrac{1}{100}F_{car}=\dfrac{5000\;\rm N}{100 } =\color{red}{\bf 50} \;\rm N$$
