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. The reliability used was 90%, the overall standard deviation was 0.35, initial PSI was 4.7, the TSI was 2.5 and the soil resilient modulus was 2582 lb/in2. If the road has three lanes in the design direction (and was conservatively designed), for how many years was the pavement designed to last?