a=3+cb\displaystyle a = \frac{3 + c}{b}a=b3+c
Show that ab=3+cab = 3 + cab=3+c.
Make b b\,b the subject of the formula.
210 exam-style questions on Eduqas GCSE Maths Changing the Subject of a Formula. Each one has a worked solution and a mark scheme showing where the marks go.