10.53 Calculate the estimate for the standard error of difference between two independent means for each of the following cases:

a. s2 1  12, s2 2  15, n1  16, and n2  21

b. s2 1  0.054, s2 2  0.087, n1  8, and n2  10

c. s1  2.8, s2  6.4, n1  16, and n2  21