The 8th term of an arithmetic sequence is 12.5 and the 13th term is 20. What is the 25th term?

From the 8th to the 13th there are five numbers, and the difference between the 8th and the 13th is 20-12.5=7.5, so the difference between two neighboring number is 7.5:5=1.5

from the 13th and the 25th there are 12 numbers, so the total difference is 12*1.5=18

so the 25th term is 20+18=38