Question 975926
0.25 + 0.10 (x-4) <+ 2.10; x= an integer number of minutes.  Need to subtract 4, because the first four are paid for with the 0.25 charge.  Need an integer, because fractional minutes count as a full minute.

0.25+ 0.10x -0.40 <=2.10
-0.15 +0.10 x<=2.10
0.10x <=2.25  This is an alternative.