To study the effect of curing temperature on shear strength of a certain rubber compound, 80 specimens were cured at 150oC and 95 were cured at 130oC. The specimens cured at 150oC had an average shear strength of 620 psi, with a standard deviation of 20 psi. Those cured at 130oC had an average shear strength of 750 psi, with a standard deviation of 30 psi. Determine a 95% confidence interval for the difference between the mean shear strength of specimens cured at the two temperatures.