![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
The equation is f + 9 = 20.
\(Apply subtraction property of equality: If a = b, then ![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=c84f635c23b14d1aade7a696c0a79913.png\")
)
f + 9 – 9 = 20 – 9 (Subtract 9 from each side)
\f = 20 – 9 (Apply additive inverse property: 9 – 9 = 0)
\f = 11 (Subtract: 20 – 9 = 11)![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step2.JPG\")
Check:
\To check the solution substitute f = 11 in original equation.
\11 + 9 = 20
\20 = 20 (Add: 11 + 9 = 20)
\The equality is true.![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")
The value of f = 11.