1. **State the problem:** We need to find the value of $a$ such that the equation $3(a + 5) - a = 23$ is true. 2. **Write the equation:** $$3(a + 5) - a = 23$$ 3. **Apply the distributive property:** $$3a + 15 - a = 23$$ 4. **Combine like terms:** $$3a - a + 15 = 23$$ $$2a + 15 = 23$$ 5. **Isolate the term with $a$ by subtracting 15 from both sides:** $$2a + \cancel{15} - \cancel{15} = 23 - 15$$ $$2a = 8$$ 6. **Solve for $a$ by dividing both sides by 2:** $$\frac{2a}{\cancel{2}} = \frac{8}{\cancel{2}}$$ $$a = 4$$ 7. **Check the answer by substituting $a=4$ back into the original equation:** $$3(4 + 5) - 4 = 3(9) - 4 = 27 - 4 = 23$$ This confirms that $a=4$ is correct. **Final answer:** $a = 4$ (Option D)