Now Tim gets $500 after it $45 was added to what he had last week
That means that
"What Tim earned last week" + $45 = $500
Subtract $45 from $500
$500-$45= $455
If you're not sure check your work
If I make $455 now and next week I get $45 more next week
$455+$45=$500
Next week I make $500