You can set up a proportion since they will be similar triangles. Similar triangles have the same ratio for corresponding sides. The old tent is an isosceles triangle, two of the sides are equal(10 ft), the new one is said to be similar, but with two equal sides of 16 ft instead. We want to find the base of the new triangle, so we can set up a proportion:
P.S. if im wong im really sorry, its been awhile since ive had to do that. But honestly i think its D. also comment on this if im right or wrong pls, id like to know.