He steps to derive the quadratic formula are shown below:

step 1 ax2 + bx + c = 0
step 2 ax2 + bx = - c
step 3 x2 + b over a times x equals negative c over a
step 4x2 + b over a times x plus b squared over 4 times a squared equals negative c over a
step 5 x2 + b over a times x plus b squared over 4 times a squared equals negative 4 multiplied by a multiplied by c, all over 4 multiplied by a squared plus b squared over 4 times a squared
step 6 the square of the quantity x plus b over 2 times a equals b squared minus 4 multiplied by a multiplied by c, all over 4 times a squared
step 7 x plus b over 2 times a equals plus or minus square root of the quantity b squared minus 4 times a times c over 4 times a squared equals plus or minus square root of b squared minus 4 times a times c, all divided by 2 times a
step 8 x = -negative b over 2 times a plus or minus square root of b squared minus 4 times a times c, all divided by 2 times a
step 9 x = negative b plus or minus square root of b squared minus 4 times a times c, all divided by 2 times a which of the following is the first incorrect step?
a. step 4

b. step 6

c. step 7

d. step 8