To find the height of the ball after 7.5 seconds, we need to evaluate the function \( h(s) = -s^2 + 10s + 3 \) at \( s = 7.5 \).
Let's calculate \( h(7.5) \):
\[ h(7.5) = - (7.5)^2 + 10 \cdot 7.5 + 3 \]
First, calculate \( (7.5)^2 \): \[ (7.5)^2 = 56.25 \]
Now substitute this value back into the equation: \[ h(7.5) = -56.25 + 10 \cdot 7.5 + 3 \]
Calculate \( 10 \cdot 7.5 \): \[ 10 \cdot 7.5 = 75 \]
Now substitute this value back into the equation: \[ h(7.5) = -56.25 + 75 + 3 \]
Now perform the addition: \[ h(7.5) = -56.25 + 75 = 18.75 \] \[ h(7.5) = 18.75 + 3 = 21.75 \]
So, the height of the ball after 7.5 seconds, \( h(7.5) \), is:
\[ \boxed{21.75} \]