greatest common factor (or denominator) is 6,
least common multiple is 180
hmm
(note: I spent like 30 mins trying to use a math only of finding the values but it didn't work so I did a force brute and elimination method explained below)
so
a and b must be multiples of 6
so list all the multiples of 6
wait
180=6*30 and 30's factors are 1,2,3,5,6,10,15,30 so only list the numbers that are the result of multiplying 6 and any of those numbers in that list (so we can have the lcm of 180)
so
6*1=6
6*2=12
6*3=18
6*5=30
6*6=36
6*10=60
6*15=90
6*30=180
these are our possible candidates for the 2 numbers
now we must find the pair that has a GCD of only 6
doing the math is long and tedious so do it yourself (trial and error)
we see that our choices that fulfill both requirements (GCD of 6 and LCM of 180) are
90&12
60&18
30&36
sum them to find the least one
90+12=102
60+18=78
30+36=66
the least possible sum is 66