`n:7=x+5`
`n:8=y+3`
`n:13=z+9`
`n=7.x+5`
`n=8.y+3`
`n=13.z+9`
`=>n=7.x+5 (x in N)=>12n=7.x_1 +4=>(12n-4) vdots 7`
`=>n=8y+3 (y in N)=>12n=8y_1 +4=>(12n-4) vdots 8`
`=>n=13z+9 (z in N)=>12n=13.z_1 +4=>(12n-4)vdots 13`
`=>12n-4 vdots7;8;13`
`=>12n-4 in BCNN(7;8;13)=728`
`=>12n-4=728`
`=>12n=732`
`=>n=732:12`
`=>n=61`