Convert 3684 to standard form

Let's make an equation.
So let's have t as our mystery number.
The word "is" shows where the equal sign will be.
Let's find out what the first half of the equation will be.
Twice the square of a certain positive number.
2t²
Now the second half.
144 more than twice the number.
2t+144
2t²=2t+144
Let's subtract 2t from both sides.
2t²-2t=144
Let's divide both sides by 2.
t²-t=72
By looking at the equation, I can tell that it is less than 10. The number may be 9.
81-8=72
The number is 9.
Let's plug it in.
2(81)=144+18
162=162
There's also another way to solve it by plugging in two expressions on a calculator and searching for when they intercept (shown in a picture below).
The number is 9.