Ahmad used sticks to form the following figures.

1. Find the number of triangles for Figure 4 by observing the constant difference

The number of triangles increases by $2$ each time ($4 - 2 = 2$, $6 - 4 = 2$).
For Figure 4, number of triangles = $6 + 2 = 8$.

2. Find the number of sticks for Figure 4 by observing the constant difference

The number of sticks increases by $7$ each time ($15 - 8 = 7$, $22 - 15 = 7$).
For Figure 4, number of sticks = $22 + 7 = 29$.

1. Find the general formula for the number of sticks in Figure $n$

The number of sticks forms an arithmetic progression: $8, 15, 22, \dots$
The common difference is $15 - 8 = 7$.
The number of sticks in Figure $n$ is $8 + 7(n - 1) = 7n + 1$.

2. Set up and solve the equation for the given number of sticks

Let $7n + 1 = 2507$.
$7n = 2506$
$n = \frac{2506}{7} = 358$