Question

1+6+11+16+.............+x = 148

Answer 1

1+6+11+16+111+x=148
145+x=148
x= 148-145
x=3

Answer 2

148=n/2(2+(n-1)5)
296=(5n-3)n
5n^2-3n-296=0
5n^2-40n+37n-296=0
5n(n-8)+37(n-8)=0
(n-8)(5n+37)=0
n-8=0
n=8
X=a+(n-1)d
    =1+(8-1)5=1+35=36
X=36