Answer:
His teacher advised it because he did not have time to tutor Euler privately
Explanation:
We know that
Euler in his autobiographical writings, talked about his tutor Johann Bernoulli. He claimed that his tutor was a very busy person who refused to give him private lessons, but gave him many valuable tips to start reading and studying more advanced math books on his own.
therefore
His teacher advised it because he did not have time to tutor Euler privately