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? step 1 step 3 step 4 step 2