We know that the number of ushers (\( U \)) is directly proportional to the number of spectators (\( S \)). This can be expressed as:
\[ U = kS \]
where \( k \) is the constant of proportionality.
From the information provided, when there are 510 spectators, there are 17 ushers. We can use this to find \( k \):
\[ 17 = k \times 510 \]
To find \( k \), we can solve for it:
\[ k = \frac{17}{510} = \frac{1}{30} \]
Now that we have found \( k \), we can use it to find the number of ushers needed for 1,050 spectators:
\[ U = k \times S = \frac{1}{30} \times 1050 \]
Calculating this gives:
\[ U = \frac{1050}{30} = 35 \]
Therefore, the number of ushers needed for 1,050 spectators is 35 ushers.