My arithmetic sequence : 4, 8, 12, 16, 20 (determine $t_{50}$)

$t_{50}$ = $t_1$ + ( $n$$1$ )( $d$ )

$t_{50}$ = $4$ + ( $50$$1$ ) ( $4$ )

$t_{50}$ = $4$ + $196$

$t_{50}$ = $200$

Finding the sum of 50 terms :

$S_{50}$$\frac{n}{2}$ ($t_1$ + $t_n$ )

$S_{50}$ = $\frac{50}{2}$ ($4$ + $200$ )

$S_{50}$ = $25$ ( $204$ )

$S_{50}$ = $5100$