This sequence is doubling the sequence and adding half. When n is your number, you could find the next number in your sequence by plugging in the number:
2n+0.5n
To find the 4th term, we need to plug in 50.
2*50+0.5*50=125
Now, we need to find the 5th term, so we plug in 125.
2*125+0..5*125=312.5
To find the 6th term, we plug in 312.5.
2*312.5+0.5*312.5=781.25
So, the next 3 terms are 125, 312.5, and 781.25
