Answer :
Given in the question:
a.) On a model of a castle, 1 inch equals 83 feet.
b.) The model is 10.5 inches wide.
To be able to determine the actual width of the castle, we will be applying ratio and proportion.
We get,
[tex]\text{ 1 in. : 83 ft. = 10.5 in. : x}[/tex]Where,
x = the actual width
Let's now solve,
[tex]\text{ 1 in. : 83 ft. = 10.5 in. : x }\rightarrow\text{ }\frac{1\text{ in.}}{83\text{ ft.}}\text{ = }\frac{10.5\text{ in.}}{x}[/tex]