Just the cardinal number 900 —
九 (nine) +
百 (hundred). To talk about 'nine hundred X', insert a measure word:
九百个人 (jiǔbǎi gè rén, 900 people),
九百块钱 (jiǔbǎi kuài qián, 900 yuan). Note: when the number stands alone before
块/yuan in casual speech, the
钱 can be dropped.
