2.7 In Problem 2-6, if the base and subgrade are combined as one layer, as shown in Figure P2.7a, what should be the equivalent elastic modulus of this combined layer so that the same ten- sile strain at the bottom of HMA can be obtained? If the HMA and base are combined as 40,000 lb 40,000 lb 150 psi E₁ =400,000 psi &, given 5.75 in. E₁ = ? E₂ = ? FIGURE P2.7 (a) 150 psi &₂ given E₂ = 10,000 psi (b) 28.75 in. one layer with the same total thickness of 28.75 in., as shown in Figure 2.7b, what should be the equivalent elastic modulus of this combined layer so that the same compressive strain on the top of subgrade can be obtained? [Answer: 20,000 psi, 35,000 psi]