Çözüldü Line Equation (8th Grade)

The data showing the revenue based on the number of T-shirts sold at a store is provided below:
The Number of Sales: x = {1, 2, 3, ...}
Revenue (TL): y = {350, 700, 1050, ...}
What is the equation showing the linear relationship between the number of T-shirts sold and the revenue generated?

(y - 350) / (350 - 700) = (x - 1) / (1 - 2) ⇒ y = 350·x.

Note:
350 = 1·350
700 = 2·350
1050 = 3·350
...

Source (Turkish): "Matematik, Konu Anlatımlı Föyler", Bilfen Yayıncılık, 8. Sınıf, FÖY 29, Test 1, Soru 2