Answer:
A
Step-by-step explanation:
compare the coefficients of the x-term; you want to see the number 5
5x, constant of proportinality = 5
10/5x, constant of proportinality = 2
5/25x, constant of proportinality = 1/5
1/2x, constant of proportinality = 1/2
So, A is correct.
Let me know if this helps!
