ANSWER:
If two quantities are equal to the same quantity, then they are equal to each other: if a = b and b = c, then a = c
SOLUTION:
Given that, two quantities are equal two to the same quantity.
Suppose the two quantities be x and y
Now, imagine that, both x and y are equal to a third quantity.
Let the third quantity be z.
Then, according to our assumption x = z and y = z
Then, we can write it as x = and z and z = y ⇒ x = y
Which means the first two quantities are equal.
Now, we are also given that, a = b and b = c, then just like above assumption, here a equals to c i.e. a = c
Hence, If two quantities are equal to the same quantity, then they are equal to each other: if a = b and b = c, then a = c