First one:
Not equivalent, because 3 is also being multiplied with b, since 3 is being multiplied against a and b.
So therefore, to be equal, it must be 3a + 3b.
Second One:
Yes, it is equal, because 4 is being distributed to everything, 2y * 4 -> 8y and 4 * x-> 4x
I hope this sorta helped!
