In order to find the length of the base we have to find x.
Now we know that an isosceles triangle has two sides that are congruent and a base.
We know that the two sides are x +1 and -x + 7
We can figure out x by making these two equal each other.
x + 1 = -x + 7 *first step is to get you x's together*
+x = +x *Now the x's cancel on the right side. and group them on the left*
2x + 1 = 7 * Now subtract 1 form both sides*
- 1 = - 1 * Solve the right side.
2x = 6 * divide both sides by 2 to isolate the x to be alone*
÷2 = ÷2 * solve the right side.
x = 3
Now we know x lets plug in that number for the Length of the base.
3(3) - 3
9 - 3 = 6
So your answer is B. 6
Good Luck! :)