when a = b and c = d which of the following equations must be true?
Verify each option
option F
a+b=c+d
a = b and c = d
so
a+a=c+c
2a=2c ------> is not true
option G
a+d=b+c
a = b and c = d
a+c=a+c -----> is true
option H
a+c=a+b
c=b -----> is not true
option J
a-c=d-b
a = b and c = d
a-c=c-a -----> is not true
option k
ad=cd
a = b and c = d
ac=c^2 -----> is not true
therefore
the answer is
option G