75-66:(4+30:(7+56:(75-x)))=120:30
75-66:(4+30:(7+56:(75-x)))=4
75-4=66:(4+30:(7+56:(75-x)))
66:(4+30:(7+56:(75-x)))=71
66:71=4+30:(7+56:(75-x))
66/71-4=30:(7+56:(75-x))
-218/71=30:(7+56:(75-x))
30:(-218/71)=7+56:(75-x)
30*(-71/218)=7+56:(75-x)
-1065/109=7+56:(75-x)
-1076/109-7=56:(75-x)
-1839/109=56:(75-x)
56:(-1839/109)=75-x
56*(-109/1839)=75-x
-6104/1839=75-x
x=75+6104/1839
x=75+3 587/1839
x=78 587/1839
