Explanation

Let's denote the cost of one pizza as P and the cost of one donut as D.

From Farhan's purchase:

4P + 3D = 1670 ... (1)

From Hamid's purchase:

6P + 2D = 2280 ... (2)

We can multiply equation (1) by 2 and equation (2) by 3 to make the coefficients of D equal:

8P + 6D = 3340 ... (3)

18P + 6D = 6840 ... (4)

Now, subtract equation (3) from equation (4):

10P = 3500

P = 350