Please explain a little bit further

Question

4(5^(2n+1))-10(5^(2n-1))/ ( 2(5^n))
= 2(5^(2n-1) ) ( 2(5^2 - 5(1) )/2(5^n))

= 5^(n-1) (50 - 5)
= 225 (5^(n-1) )