At Barlow School: 4 / 9 * 873 = 388 boys.
At Willow School: 2 / 3 * 630 = 420 girls.
At Willow School: 630 - 420 girls =210 boys.
Barlow School has =388 boys
Willow School has =210 boys. So:
388 - 210 = 178 more boys at Barlow School than Willow School.
