How many altars did Balaam tell Balak to build before his first oracle?

Answer: Seven

Balaam asked for seven altars with seven bulls and seven rams, and Balak and Balaam offered a bull and a ram on each altar.

“Then Balaam said to Balak, “Build for me seven altars here, and prepare for me seven bulls and seven rams.” So Balak did as Balaam had instructed, and Balak and Balaam offered a bull and a ram on each altar.”— Numbers 23:1-2 (BSB)