Given that Macy wants to construct an isosceles triangle, with the unique angle being 40° it implies that for the triangle to be isosceles, the base angles should be the same. The size of the base angles will be:
(180-40)/2=70
given that that the base is 6 cm, Macy can only form 1 triangle with these dimensions.
The length of the other sides will be found using sine rule
a/sin A=b/sin B
a=6 cm
A=40°
b=?
B=70
hence:
6/sin 40=b/sin 70
b=(6sin 70)/sin40
b=8.77 cm