If Terry’s cup holds x ounces then Toby’s holds 8x ounces and Tom’s holds x+5 ounces. Together the cups hold x+8x+x+5=35 ounces.
Therefore 10x+5=35, 10x=30 and x=3. So Terry’s cup holds 3 ounces, Toby’s 24 ounces and Tom’s 8 ounces.
Toby’s cup holds 24 ounces of water.