I need to have a collum A1 equaling the sum of collum B1 and C1. When I have
the answer in A1 and I type new value in B1 or C1, A1 must increase its value
by the number added. eg, B1 20 C1 30 A1 50. Now I change B1 to 30 and A1
gives me 80. Can this be done?