If matrix A has row 1 + row 2 = row 3, show that A is not invertible Linear Algebra 2-5-7

Introduction to Linear Algebra
Strang 4th edition
2-5-7
(Important) I f A has row 1 + row 2 = row 3, show that A is not invertible:
(a) Explain why Ax = (1,0,0) cannot have a solution.
(b) Which right sides (bI , b2 , b3) might allow a solution to Ax = b?
(c) What happens to row 3 in elimination?

[alexcosta]

why will row 3 be 0 when we do elimination???😕