Assuming that the mileage is s and the cost is x, when s is greater than 10, it will be charged according to the charging standard.
X =10+(10-3) * 2+(s-10) * 3, taking S=20 as an example,
X= 10+ 14+30=54 yuan.
If you take it in two steps, it will cost you.
2*( 10+ 14)=48 yuan,
So it will save money to fight separately.