How could you draw a model to show the relationship between feet and inches?

Express the following as a function of a single angle, cos(60) cos(-20) - sin(60) sin(-20)

The standard distance between studs in a house is 1.5 feet. if you have a set of blueprints for a house that mark every 1.5 feet with 2 in., by how many inches will a 13-foot wall be represented?

Aquadratic equation in standard from is written ax^2= bx+c, where a,b and c are real numbers and a is not zero?