execl how to addition and subtraction

Before the school now has returned to his old teacher.Forgotten now.Who can tell me.
Xiangxi to the point

If you want to be in the C1 results of A1 + B1, C1 only in the inside input “= A1 + B1” on the line in the post-arithmetic is an equal sign, ECXEL equal sign is the former, and arithmetic to do the same:
= a1-b3
= d3 + f4
= 67-6
= 68 +65
= 45 * 8
= e3 * 4