Consider an acrylic sheet of thickness L = 5 mm that is used to coat a hot, isothermal metal substrate at Th = 300 degrees C. The properties of the acrylic are ρ = 1990 kg/m^3, c = 1470 J/(kg*K), and k = 0.21 w/(m*K). Neglecting the thermal contact resistance between the acrylic and metal substrate, determine how long it will take for the insulated back side of the acrylic to reach its softening temperature, Tsoft = 90 degrees C. The initial acrylic temperature is Ti = 20 degrees C.