`a) 595959/454545-14141414/15151515`
`=(59xx10101)/(45xx10101)-(14xx1010101)/(15xx1010101)`
`=59/45-14/15`
`=(59-3.14)/45`
`=(59-42)/15`
`=17/15`
`b) 50/19. 38/25<x<69/17+33/17`
`<=> (2.25.2.19)/(19.25)<x<(69+33)/17`
`<=> 4<x<102/17`
`<=> 4<x<6`
Do `x∈N`
`=>x=5`
Vậy `x=5`
$\color{black}{\heartsuit }$