First plug in 2 for r like so:
-9(2) - 7
To solve this you must use the rules of PEMDAS (Parentheses, Exponent, Multiplication, Division, Addition, Subtraction)
REMEMBER: IF NOT APPLICABLE TO THE EQUATION YOU MAY SKIP THAT STEP IN PEMDAS .
First we have multiplication:
-9(2) - 7
-9(2) = -18 <<< When multiplying a negative and positive number together you will multiply normally and the answer will have a negative sign
-18 - 7
Now for the subtraction:
-18 - 7 <<< When subtracting with a negative number you will do something called "Same-Add-Opposite." This means that you will keep the first number in the expression (in this case that is -18) the same. Then turn the subtraction sign into an addition sign. Finally you will take the "opposite" sign of the second number. When I say "opposite sign" I mean that if this number is positive it will become negative. If it was negative it will become positive.
Here is your expression after applying same - add - opposite:
-18 + (-7)
-25
Hope this helped!
~Just a girl in love with Shawn Mendes