9

`72 : 12 * 9 = 6 * 9 = 54`
`(540 - (68 - 5)) : 7 = (540 - 63) : 7 = 477 : 7 = 68`
`4 * 15 : 10 = 60 : 10 = 6`
`96 : 12 * 8 = 8 * 8 = 64`