Example
Alice has $8 to buy chocolate (X) and strawberries (Y).
The price of a chocolate bar is `p_X = $4` and the price of a strawberry is `p_Y = $2`.
The Marginal Rate of Transformation of a strawberry into a chocolate ibar s $$MRT = - \frac{p_X}{p_Y} = - \frac{4}{2} -2$$
So 1 chocolate bar is worth 2 strawberries.
Graphically, it corresponds to the slope of the budget line: $$ 4 X + 2 Y = 8 $$
Therefore, $$ Y = - \mathbf{2} X + 4 $$
To get 1 chocolate bar, Alice needs to give 2 strawberries.
Question
The price of a chocolate bar (X) is $49 and the price of a strawberry (Y) is $1470.
How many strawberries can Alice get if she forgoes a chocolate bar?
A chocolate is worth `\frac{49}{1470} = 1 / 30` strawberries.