Step 4: Solve the integral \( \int_0^6 \sqrt{1 + 27x} \, dx \). Use a substitution method: let \( u = 1 + 27x \), so \( du = 27 \, dx \). Adjust the limits of integration accordingly: when \( x = 0 \), \( u = 1 \); when \( x = 6 \), \( u = 163 \). The integral becomes \( \frac{1}{27} \int_1^{163} \sqrt{u} \, du \).