Question 62355
<b>how could i make a system of equations (2) for this problem: sue is 4 years younger than sally. in 3 years sally will be twice as old as sue. how old are they now?</b>

Let S = Sue's Age
Let A = Sally's Age

Then, {{{S=A-4}}}.
Also, {{{A+3=2*(S+3)}}}.

Then, {{{A+3=2*(A-4+3)}}}.
Or, {{{A+3=2*(A-1)}}}.
Or, {{{A+3=2*A-2}}}.
Or, {{{A+5=2*A}}}.
Or, {{{A=5}}}.
So, Sue is 4 years younger than Sally, so Sue is one year old: {{{S=1}}}.

Let's verify the answer:

If Sue is 1 year old then Sally is 5 years old. In 3 years Sue will be 4 years old and Sally will be 8 years old so, indeed, Sally will be twice as old as Sue.