College Algebra
posted by Kristen .
Solve for the specified variable in each formula or literal equation
Sn=n(a1+an/2) for n (sequences)

Your formula is not correct, it should be
Sn = n(a + l)/2 or (n/2)(first + last)
your equation makes no sense 
I like to change this(1023.065476) whole number into a mixnumber to find the volume of the sphere (6 1/4 in) using 22/7 for pie.

V= 4/322/7r^ 3
v= 4/3 *22/7*(6 1/4 in)^3
v=3/4 * 22/7 * 15625/64
v= 1023.065476 how to change to a mixnumber?