Lover of Math

There was a math student who used to spend most of his time exploring the numbers he had once went to his grandmother's house which is in a village. After few days he returned to his hometown which was y km far from his grandmother's house. When his best friend inquired about the distance of the village from the town he gave this :

$x^{2} -5 x+6=0$ has a and b as its roots. where $a>b$ , and y= $\frac{[5a^{2019}-6a^{2018}]*[6ab+5(a+b)]}{5a^{2017}-6a^{2016}}$ His friend struggles to get the answer but at last figures out the answer by using simple logic. Can you figure out the value of y=?