Question 238100
This is a substitution problem.
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Given:
f(X) = 8 + X
g(X) = X - 5
d(X) = f(X) - g(X), find d(X)

All you need to do now is plug (8 + X) in for f(X) and plug (X - 5) in for g(X) into the d(X) equation.

{{{d(X) = f(X) - g(X)}}}
{{{d(X) = (8 + X) - (X - 5)}}} rewrite the equation
{{{d(X) = 8 + X - X + 5}}} Add like terms
{{{highlight(d(X) = 13)}}}