The work of a student to solve a set of equations is shown: equation a: y = 4 − 2z equation b: 4y = 2 − 4z step 1: −4(y) = −4(4 − 2z) [equation a is multiplied by −4.] 4y = 2 − 4z [equation b] step 2: −4y = 4 − 2z [equation a in step 1 is simplified.] 4y = 2 − 4z [equation b] step 3: 0 = 6 − 6z [equations in step 2 are added.] step 4: 6z = 6 step 5: z = 1 in which step did the student first make an error? (5 points)