What is the measure of one of the base angles of an isosceles triangle if the measure of the vertex angle is 98 degrees ?

Triangles have 3 angles totalling 180 degrees.
An isosceles triangle has base angles equal so 2*base angle + vertex = 180.

180 - 98 = 2 *base angle
82 = 2 * base angle
Each base angle = 41 degrees.