Final answer:
The value of the expression 9x - y for x=5 and y=4 is calculated by substituting the values into the expression, resulting in a value of 41.
Step-by-step explanation:
To evaluate the algebraic expression 9x - y for x = 5 and y = 4, we substitute the given values into the expression.
So, we replace x with 5 and y with 4 and get:
9(5) - 4 = 45 - 4 = 41.
Therefore, the value of the expression 9x - y when x = 5 and y = 4 is 41.