One billion
Since this is a British site you should know that 1 billion is called a thousand million by many in the British Isles.
Easiest way for me is to convert to scientific notation
1,000 becomes 1x10^3 and !,000,000 becomes 1x10^6
then multiply 1x1 and add powers gives you 10^9
answer 1,000,000,000
write them as
10³ × 10⁶
= 10³⁺⁶
= 10⁹ = 1,000,000,000