Consider that the sum of the length of the segments DE and EF is equal to the length of the segment DF. Then, by using the given expression for each segment, you can write:
(3x - 1) + (13) = 6x
Solve the previoud equation as follow:
(3x - 1) + (13) = 6x cancel out parentheses
3x - 1 + 13 = 6x simplify like terms left side
3x + 12 = 6x subtract 6x both sides and 12 both sides
3x - 6x = - 12 simplify left side
-3x = -12 divide by -3 both sides
x = -12/(-3)
x = 4
Hence, the value of x is x = 4
