Find a general formula for each arithmetic sequence

1. 8th term is -20; 17th term is -47
2. 12th term is 30; 22nd term is 50

The n-th term of an arithmetic sequence is a+(n-1)d where a is the first term and d is the common difference.
1) a+7d=(-20); a+16d=(-47)
subtracting first from second we get 9d=(-27) or d=(-3)
plugging that d into a+7d=(-20), we get a=1
so general formual is 1-3(n-1)=4-3n

2) a+11d=30; a+21d=50
subtracting 10d=20 or d=2
plugging d=2 in a+11d=30, we get a=8
so general formula is 8+2(n-1)=6+2n