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