Question

Please help. It’s worth 4 marks

Answer 1

`f=(3+4d)/(3+d)`

Explanation:

`d= (3(1-f))/((f-4)) \\(f-4)d=3-3f\\f-4=(3-3f)/(d) \\f=(3-3f+4d)/(d) \\f+(3f)/(d) =(3+4d)/(d) \\fd+3f=3+4d\\f(d+3)=3+4d\\f=(3+4d)/(3+d)`