Concept:Represent numbers as multiples of a common factor and use LCM to find the factor.Explanation:Let the numbers be 6x and 13x, where x is a positive integer.Since 6 and 13 are coprime, their LCM is 6×13=78.Thus, LCM of 6x and 13x is 78x.Given LCM = 312, so 78x=312.Solve: x=312/78=4.Numbers: 6×4=24, 13×4=52.Sum: 24+52=76.Answer:76