23-45+12=?     4567-(45+?)=67    3445263-7654-7356=?                                                                                                            

1)23-45+12=-22+12=-10

2)4567-(45+?)=67 

4567-45-?=67

 4522-?=67

?=4522-67

?= 4455

3)344263-7654-7356= 3437609-7356=3430253

23-45+12=-10

4567-(45+?)=67

45+?=4567-67

45+?=4500

?=4500-45

?=4455

4567-(45+4455)=67

3445263-7654-7356=3430253