The electrical resistance in ohms of a certain thermometer varies with temperature according to the approximate law: `R=R_o[1 + a (T- T_o)] `. The resistance is 101.6 `ohom` at the triple-point of water 273.16 K, and 165.5 `ohm` at the normal melting point of lead (600.5 K). What is the temperature when the resistance is `123.4 ohm`