A college has 3,200 undergraduate students and 800 graduate students. Researchers are interested in the amount of money spent in a year on textbooks by these students. Initially, simple random samples of 30 undergraduate students and 30 graduate students were taken. The sample standard deviations for amounts spent were $40 and $58, respectively. A 90% confidence interval for the overall population mean that extends $5 on each side of the sample point estimate is required. Estimate the smallest total number of additional sample observations needed to achieve this goal.