Each term is equal the preceding term plus 3. Therefore the next term is 13 and the difference is +3.
You add +7 to both sides and then divide by 9 to get the x alone.
For this case we propose a system of equations. We have to:
x: Let the variable that represents the number of dimes
y: Let the variable that represents the number of quaters
We know that:
One dime equals 10 cents, $0.10
A quater equals 0.25 cents, $0.25
According to the statement we have:

We multiply the first equation by -0.10:

We have the following equivalent system:

We add the equations:

Approximately 3 quater coins

And two dimes
Answer:
3 quater
2 dimes
Yes you can assume they are similar because the sides that correspond with one another are half of the big triangles measurements. 16/2=8 12/2=6 etc.