Let S=1+45+752+1053+... (1) Above given series is an AGP with common ratio 15
Multiply by common ratio to equation 1.
S5=15+452+753+... (2)
Subtract equation 2 from equation 1
S−S5=1+35+352+353+...
4S5=1+3(151−15)
=1+3(1545)=1+34=74
4S5=74
S=3516,
16S=35