To know the answer to this we work our way backwards.
First we'll have a proportion since we know Jiayi ended up with 75 markers and the ratio of Stanley's markers to Jiayi's is now 2:3. We let the number of Stanley's markers at the end be denoted by x and solve the proportion:



We know that Stanley had 50 markers by the end, and since he let Jiayi borrow 50 markers, then he should've had 100 markers at the start.
ANSWER: Stanley started with 100 markers.