Some country interpolate insurance between different tires instead. So, if $0 at $20000 income, and $5000 at $40000 income. A person with $21000 income will n

Some country interpolate insurance between different tires instead. So, if $0 at $20000 income, and $5000 at $40000 income. A person with $21000 income will need to pay $0 + ($21000 - $20000) / ($40000 - $20000) * $5000, a.k.a $250