11, 15, 19, 23, 27….

Common difference = +4

 

Find t_{50}:

t_n = t_1 + (n – 1)d

= 11 + (50 – 1) 4

= 11 + (49)4

= 207

 

S_n = (t_1 + t_n) \frac{n}{2}

= (11 + 207)\frac{50}{2}

= (218) 25

= 5450