P and Q start running in opposite directions (towards each other) on a circular track starting at diametrically opposite points. They first meet after P has run for 75m and then they next meet after Q has run 100 m after their first meeting. Assume that both of them are running a constant speed. The length of the track (in metre) is:

a)70 b)175 3)250 4)350

my solution 

let p and q be speed of P and Q respectively and 2d be circumference
since both start at diametrically opposite points so they meet at same time that is 

75/p = (d-75)/q .....1

and Q has run 100m after first meeting so P will run 2d - 100 for next meeting 

hence 100/q = (2d-100)/p ......2

solving 1 and 2 d is 125m , so 2d = 250m 

is my solution correct or wrong ?
while answer is 350 
here is the link 
<http://www.lofoya.com/Aptitude-Questions-And-Answers/Time-Speed-and-Distance/l1p6.htm>
check question 27 with solution