To find the height of the ball after 7.5 seconds, we can substitute \( s = 7.5 \) into the function \( h(s) = -s^2 + 10s + 3 \).
Let's calculate it step by step:
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Substitute \( s = 7.5 \) into the function:
\[ h(7.5) = - (7.5)^2 + 10(7.5) + 3 \]
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Calculate \( (7.5)^2 \):
\[ (7.5)^2 = 56.25 \]
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Now substitute that back in:
\[ h(7.5) = -56.25 + 10(7.5) + 3 \]
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Calculate \( 10(7.5) \):
\[ 10(7.5) = 75 \]
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Now substitute that back in:
\[ h(7.5) = -56.25 + 75 + 3 \]
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Combine these:
\[ h(7.5) = -56.25 + 75 = 18.75 \]
\[ h(7.5) = 18.75 + 3 = 21.75 \]
So, the height of the ball after 7.5 seconds is:
\[ \boxed{21.75} \]