4. Simplify the following expression: (15a^2) / a - 2a * 2

Let's break down the expression step by step! Start with the division: \(15 a^{2} \div a\) simplifies to \(15a\) because dividing \(a^{2}\) by \(a\) reduces the exponent by one. Now, tackle the second part: \(-2a \times 2\) gives us \(-4a\). Now, put it all together: you have \(15a - 4a\). Simplifying that results in \(11a\). So, the simplified expression is: \[ 11a \]