sorry for bothering,but could someone work/explain this out for me .

Question

Joseph has $1.45 worth of nickels and dimes. He has a total of 17 nickels and dimes altogether. Determine the number of nickels and the number of dimes that Joseph has.

Answer 1

N+D =17

5N+10D =145

5N +5D =5(17) = 85

subtract last equation from 2nd equation

5D = 60

D = 60/5 = 12 Dimes

N= 17-12 = 5 Nickels

5(5)+10(12) = 25+120 = 145