arithmetic
posted by bob .
In a certain arithmetic sequence, t6 + t15 = –141 and the common difference is –7.
What is the first term of the sequence?
explain how to do this please

you know t6 = a+5d
you know t15 = a+14d
so a+5d + a+14d = 141
don't you know d= 7 ???
take over ....