Maths Equation

Louise had saved $73 to buy a bike but she needed $92. How much more did she need to save?

$73 + ? = $92

$73 + $20 = $93

$93 - $1 = $92

$73 + $19 = $92

$73 + ? = $92

$73 + $20 = $93

$93 - $1 = $92

$73 + $19 = $92