let L is the number of large and S is the number of small, thren we have: L - 3S = 30 (1) and S/L=1/6 (2)
solving the (1) for L we get L = 30 + 3S substituting this value of L to (2) we get S/(30+3s) = 1/6
and 30+3S = 6S --->>> 30 = 3S And S = 10 sustituting this value os S to (1) we get L=60