We have to calculate the percent of error of the guess.
The guess was 140 and the actual number was 155.
The percent of error will be the absolute value of the difference between the guess and the actual number, divided by the actual number as it is relative to it.
Then, this proportion, will be multiplied by 100% to express it as perecentage.
We can then calculate this as:
[tex]\begin{gathered} e=\frac{|G-A|}{A}\cdot100\% \\ e=\frac{|140-155|}{155}\cdot100\% \\ e=\frac{|-15|}{155}\cdot100\% \\ e=\frac{15}{155}\cdot100\% \\ e\approx0.096774\cdot100\% \\ e\approx9.68\% \end{gathered}[/tex]Answer: the percent of error is 9.68%.