To solve the problem, we can use the concept of direct proportionality. The relationship between the number of ushers \( U \) and the number of spectators \( S \) can be expressed as:
\[ U = k \cdot S \]
where \( k \) is the constant of proportionality.
From the information given, when there are 510 spectators, there are 17 ushers. We can use this information to find \( k \):
\[ 17 = k \cdot 510 \]
Now, solving for \( k \):
\[ k = \frac{17}{510} = \frac{1}{30} \]
Now that we have the value of \( k \), we can find out how many ushers are needed when there are 1,050 spectators.
Using the formula:
\[ U = k \cdot S = \frac{1}{30} \cdot 1050 \]
Calculating this gives:
\[ U = \frac{1050}{30} = 35 \]
So, the number of ushers needed for 1,050 spectators is 35 ushers.