What is the common denominator between 1/4 and 3/5?

An isosceles triangle has two sides of equal length, a, and a base, b. the perimeter of the triangle is 15.7 inches, so the equation to solve is 2a + b = 15.7. if we recall that the sum of the lengths of any two sides of a triangle must be greater than the length of the third side, which lengths make sense for possible values of b? select two options.