given
\(n^2+4n\) units digit is 7 and units digit of n is 7
by simplifying that n(n+4)
if n is even then units digit won't be odd so neglect 2,4,6,8 and even integers
remaining 1,3,5,9 and other odd integers without units digit 7
if we take 1 then units digit is 5
if we take 3 then units digit is 1
if we take 5 then units digit is 5
if we take 9 then units digit is 7so n will 9 and odd integers having units digit 9
now units digit of n+3 will be 2(9+3=12)
_________________
thank you
gajala
"If you like my explanation please click kudos"
Thank you for 100 kudos
for more quant problems here is the link
https://gre.myprepclub.com/forum/gre-math-book-for-the-gre-exam-2609.html