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