Question 1108116
x, days walk
y, day bike
d, total distance for x+y days

{{{5x+10y=d}}}


BETWEEN 150 AND 200 MILES
{{{150<=5x+10y}}} and {{{5x+10y<=200}}}

{{{system(30<=x+2y,x+2y<=40)}}}


{{{system(15<=x/2+y,x/2+y<=20)}}}


Just the reference lines:
{{{graph(300,300,-2,22,-2,22,-x/2+15,-x/2+20)}}}

Test any whole number value for x BETWEEN the lines, possibly including a line and see if it works for BOTH inequalities.  Possibly more than one solution possible.   You will want to test x values which are divisible by 2 leaving no remainder.