∵ a-b=3/5∴ a=3/5+b∵ b-c=3/5∴ b=3/5+c∴ a-c=6/5∴ c=a-6/5ab+bc+ac=(3/5+b)b+(3/5+c)c+a(a-6/5)= a^2 + b^2 + c^2-6/5a+3/5b+3/5c=1-3/5a+3/5b-3/5a+3/5c=1-3/5(a-b)-3/5(a-c)=1-3/5*3/5-3/5*6/5=-2/25
