Ataxi ride costs 2.75 for the first quarter of a mile and 0.85 for each susequent quarter mile

Equation would be
for the nth mile the cost would be
f(n)=(n-1)0.85+2.75
that way, for the 1st mile, the 0.85 doesn't apply
then for the next miles, it does
we can distribute it
0.85(n-1)=0.85n-0.85
so we have
f(n)=0.85n-0.85+2.75
f(n)=0.85n+1.9

the new equtation is cost for the nth mile is 0.85n+1.9