Note : Since unit of currency is not defined, I'll be using units.
Sales tax on a 15000 units car = 540 units 540 = 15000 × tax% / 100 => 540 = 15000 × tax% / 100 => 540/15000 = tax% / 100 => tax% = (540/15000) × 100 => tax% = 540/140 => tax% = 3.6
now, sales tax on a 32000 units car = 32000 × tax%/100 = 32000 × 3.6/100 = 320 × 3.6 = 1152 units therefore sales tax on a 32000 units car = 1152 units