Alexandra is preparing for the new semester of school. She buys 6 spiral notebooks, and 6 yellow highlighters for $23.06. One notebook costs

• 6 notebooks + 6 highlighters = $23.06
• 1 notebook = $3.48
• 6 notebooks = 6 * $3.48 = $20.88
• $20.88 + 6 highlighters = $23.06   | - $20.88
• 6 highlighters = $23.06 - $20.88 = $2.18
• 1 highlighter = $2.18/6 = $0.36333333333

 

1 highlighter costs $0.3633333333333

Let h be the cost of a highlighter.  We are told that:

6*h + 6*3.48 = 23.06

Subtract 6*3.48 from both sides:

6*h = 23.06 - 6*3.48

Divide both sides by 6:

h = (23.06 - 6*3.48)/6

$${\mathtt{h}} = {\frac{\left({\mathtt{23.06}}{\mathtt{\,-\,}}{\mathtt{6}}{\mathtt{\,\times\,}}{\mathtt{3.48}}\right)}{{\mathtt{6}}}} \Rightarrow {\mathtt{h}} = {\mathtt{0.363\: \!333\: \!333\: \!333\: \!333\: \!3}}$$ dollars

or, multiplying by 100 to get cents:

h = 36 cents to the nearest cent.