Since you've told us that this is an isosceles triangle, we know that the 'legs' have equal length. So we can write
x + 1 = -x + 7
Add 'x' to each side: 2x + 1 = 7
Subtract 1 from each side: 2x = 6
Divide each side by 2 : x = 3
Now, if the length of the base is 3x - 3 ,
that length is
3(3) - 3 = 6 .
