74. A wire of cross-sectional area  is

A wire of cross-sectional area  is 3mm² first stretched between two fixed points at a temperature of 20°C. Determine the tension when the temperature falls to 10°C. Coefficient of linear expansion α=10^-5 °C^-1 and  Y=2×10¹¹ N/m²

(a) 20 N                                                 (b)   30 N

(c)   60 N                                               (d)   120 N

Answer-c