D 5.31 For the circuit in Fig. E5.10, assume that Q1 and Q2 are matched except for having different widths, W1 and W2. Let Vt = 0.5 V, k'n = 0.4 mA/V^2, L1 = L2 = 0.36 um, W1 = 1.8 um, and λ = 0. (a) Find the value of R required to establish a current of 90 uA in Q1.