Solve: PDE: ut = = 4(Uxx + Uyy), (x, y) = R = [0, 3] × [0, 1], t > 0, BC: u(x, y, t) = 0 for t> 0 and (x, y) ≤ ƏR, ICs : u(x, y,0) = 7 sin(3x) sin(4πy), (x, y) = R.