For A.P nth term's formula is
An=a1+(n-1)d
5.) a4=31, a10=85
put n=4 into general term (given above)
a4=a1+(4-1)d
31=a1+3d (putting values of a4)
a1=31-3d ====> (1)
Now put n=10
a10=a1+(10-1)d
85=31-3d+9d (putting values of a10, and a1)
85=31+6d
6d=85-31
6d=54
d=54/6
d=9
Now put the value of 'd' into eq (1)
a1=31-3d
a1=31-3(9)
a1=31-27
a1=4
Thus the series will be
a2=a1+d=4+9=13
a3=a2+d=13+9=22
and so on
4,13,22,.....
And the same process for your second question
