the lowest common multiple is 5/a +7 or (5+7a)/a so in this case 7 is the biggest lcm since when doing this we find the factor of each number so 5/a is a factor. a^-1 is a factor and 7a/a is a factor then we find the highest lowest common multiple which in this case is 7

6/ab+8/a now we do 2*3/ab +2^3/a in this case we find the product of each factor with the highest power and in this case is 2^3

x+4 x^2+6x+8

for the first one x+4 we factor the second equation (x+4)(x+2) then we find the LCM so (x+2^2)(x+2)

so now we have x+4 in the first part and in the second part it is (x+2) but since that is smaller than the LCM of the first equation we must find one that equals both and in this case it is x+4 the whole LCM of both equations is (x+4)