let the number of overtime hours for john = x

So no regular hours = 172 –x

Income from overtime hours = (x)*114

Income from regular hours = (172-x)*57

Total income = 114x + (172 –x)*57 = 172*57 + 57x

As per question 15% of (172 – x) *57 = 114x

15/100 (172 +x)= 2x

15*172* – 15x = 200x

215x = 15*172

x = 12