Answer:
The savings of Sid and Tim will be in 17:9 in 6 weeks.
Step-by-step explanation:
Initial savings of Sid = £ 13
Initial savings of Tim = £ 0
For each successive week Sid saved = £ 3.5
For each successive week Tim saved = £ 3
Let us assume that after "x weeks" the amounts of Sid and Tim are in ratio 17:9.
If Sid saves £ 3.5 in one week, in x weeks he will £ 3.5x. Since he had £ 13 initially, total amount he would have in x weeks will be £ (13 + 3.5x)
If Time saves £ 3 one week, in x weeks he will save £ 3x. Since, he didn't have any money initially, in x weeks he would have saved £ 3x
The ratio of their savings in x weeks would be 17:9
So,
Sid's saving : Tim's saving = 17 : 9
Using the values of expressions, we get:

This means, the savings of Sid and Tim will be in 17:9 in 6 weeks.
I know it’s not right, I think it’s obtuse
Quickly using a calculator (or long division) reveals that 191/238=<span>0.8025=80.25%, which is close to 80%=4/5
Similarly, 106/160=0.6625=66.25%, which is close to 66.67%=2/3</span>
Solution
Step 1
The opposite angles of a parallelogram are equal:
Step 2

The equation is made true by the opposite angles theorem is
85 + y = 3y - 15
or
y = 50