2. A flexible pavement was designed to have a 6-inch sand-mix asphaltic surface, 8-inch soil-cement base and a 21-inch crushed-stone subbase (all drainage coefficients are 1.0). The pavement was designed for 800 12-kip single axles and 1600 34-kip tandem axles per day in the design direction. Traffic volume increase 3% every year. The reliability used was 90%, the overall standard deviation was 0.35, the initial PSI was 4.7, the TSI was 2.5 and the soil resilient modulus was 2582 psi. If the road has three lanes in the design direction (and was conservatively designed with a PDL 0.65), for how many years was the pavement designed for?