The following that are mathematical sentences are b,c
<h3>Answer:</h3>
13 years old
<h3>Explanation:</h3>
Let g and m represent grandfather's age now and my age now. The relation 5 years ago was ...
... g -5 = 5(m -5)
The relation in 3 years will be ...
... g +3 = 3(m +3)
Subtracting the first equation from the second, we get ...
... 8 = -2m +34
... 2m = 26 . . . . . add 2m-8
... m = 13
My age now is 13.
Recall the inclusion/exclusion principle:

which means
Answer and Explanation: The answer is in the 1st image, and the explanation is in the 2nd image.