Since the man get a fixed increment of Rs. 320 each month .
therefore this formsterm =5200 and common difference (d) =320
(i) salary for tenth month i.e., for n=10,
`a_(10)=a+(n-1)d`
`implies a_(10)=5200+(10-1)xx320`
`implies a_(10)=5200+9xx320`
`therefore a_(10) =5200+2880`
` therefore a_(10)=8080`
(ii) total earning during the first year .
in a year there are 12 month i.e., n=12,
`S_(12)=(12)/(2)[2xx5200+(12-1)320]`
`=6[10400+11xx320]`
`=6(10400+3520]=6xx13920=83520`