Answer:
a19 = -71.74
Explanation:
The general term of an arithmetic sequence with first term a1 and common difference d is ...
an = a1 +d(n -1)
The given 5th and 15th terms tell us ...
-3.7 = a1 +d(5 -1)
-52.3 = a1 +d(15 -1)
Subtracting the first of these equations from the second, we find ...
10d = -48.6
d = -4.86 . . . . . . divide by 10
The 19th term will be ...
a19 = a1 +d(19 -1)
Subtracting the 15th term from this, we find ...
a19 -a15 = 4d
a19 = 4d +a15 = 4(-4.86) +(-52.3)
a19 = -71.74