The area of one of the triangular lateral faces is
You're told that the slant height, which is the same as the height of the triangular face, is 9.8, so you have
where
is the length of the base of the triangle, which is also the same as the side length of the base of the pyramid. So
You're told that the slant height, which is the same as the height of the triangular face, is 9.8, so you have
where