u/Double-Matter6323

At the Wimbledon Championships training camp, a player’s successful serves per minute after (t) minutes of practice are modeled by:

S(t)=-3t^2+30t+12

• after how many minutes the player reaches the greatest serving rate, and
• the maximum number of successful serves per minute.

Anyone who can help me solve it?

A school is buying notebooks and pens.

• 3 notebooks and 2 pens cost £11
• 5 notebooks and 4 pens cost £19

A student says:

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Is the student correct? Explain fully.

This is a problem sent to me by my teacher. Anyone help me solve it?