I've tried to solve this but I don't seem to get anywhere.
The question states:
Tom's home is $1800$ m from his school. One morning he walked part of the way to school and then ran the rest. If it took him $20$ mins or less to get to school, and he walks at $70$ m/min and runs at $210$ m/min, how far did he run?
My attempts to solve it got me stuck here:
Any help would be appreciated!