Question 904672
a*5+b*5=20
5*(a+b)=20
a+b=4

15*a-b*15=20
1,1,4
15,-15,20
a=8/3 kph , b= 4/3 kph

check
8/3+4/3=4
12/3=4
15*8/3=120/3
60/3
120/3-60/3=20