6750 = 2*3375 = 2*5*675 = 2*5^2*135 = 2*5^3*27 = 2*3^3*5^3
151 The factors (2,3,5) of 6750 do not go into 151. so there are no common factors and therefore no LCM. 151 is prime.
108 = 2*54 = 2^2*27 = 2^2*3^3
61 The factors (2,3) do not go into 61 so there is no LCM. 61 is prime.