What constant term should be used to complete the square? x 2 - 5x + = 7

For this case we have an expression of the form:
 x ^ 2 - 5x + = 7
 To complete the square, we must add to both sides of the equation a constant of the form:
 (b / 2) ^ 2
 We have then:
 x ^ 2 - 5x + (-5/2) ^ 2 = 7 + (-5/2) ^ 2
 Rewriting we have:
 x ^ 2 - 5x + 6.25 = 7 + 6.25
 x ^ 2 - 5x + 6.25 = 13.25
 
 The constant term that should be used to complete the square is:
 6.25

Ac equals 35 cm long