Answer:
First, we need to convert the units of streamers into a common unit, so we can add the amounts hung by Gabby and her mom. 1 yard is equal to 3 feet, so we can convert the 10 yards of streamers into feet:
10 yards * 3 feet/yard = 30 feet
Now, we can add the amounts hung by Gabby and her mom:
30 feet + 8 feet + 16 feet = 54 feet
Finally, we can convert the total amount back into yards:
54 feet / 3 feet/yard = 18 yards
So, Gabby and her mom have 18 yards of streamers left.