an=a1+d(n-1)
Sn=(2a1+d(n-1))/2 * n
50=10+4(n-1)
50=10+4n-4
50=6+4n
44=4n
n=11
Sn=(20+4(11-1))/(2)*11=(20+44-4)/(2)*11=(60/2)*11=30*11=330
a1=10 , d= 4, an=50
an = a1+(n-1)*d
50 = 10 + (n-1)*4
40=4n-4
4n=44
n=11
Sn = S(11) = ((a1 + a11) * n) / 2 = ((10 + 50)*11) / 2 = 330
