(a) 32 orange marbles
the ratio of red : blue = 18 : 48 = 3 : 8 ( in simplest form )
the ratio of green : orange = 3 : 8 ( equal ratio )
divide green by 3 to obtain 1 part of ratio then multiply this value by 8 to obtain the amount of orange marbles
3 parts → 12
8 parts → 12 × = 32 orange marbles