Let's call your number n. Twice your number is 2n. The product of your number and twice your number (so n multiplied by 2n) is 128.
Set up an equation:
n × 2n = 128
2n² = 128
Divide both sides by 2:
n² = 64
Square root both sides to isolate n:
n = 8
The question asks for half your number, so just half 8:
8 ÷ 2 = 4.
Half your number is 4.