If 1+2+3+...+n=n (n+1), then 3 (1+3+5+....+79)=? Choose the correct choice from the following choices:
A) 4500 B) 4250 C) 4350 D) 4800 E) 4150

Rationale: "explanation : to solve this use the formula of ap , sn = ( n / 2 ) ( a + l ) . . . . . . . . . . . . . . . . ( 1 ) to find n , use = > tn = a + ( n - 1 ) d = > 79 = 1 + ( n - 1 ) 2 = > n = 40 use value of n in ( 1 ) then , sn = ( 40 / 2 ) ( 1 + 79 ) = 1600 ans : - 3 ( sn ) = 4800 answer : d"
Answer: D