Question 1106026
At some time a, border collie 13.4 kg
and a+4 week, border collie 17 kg
And assuming a is any ARBITRARY beginning time 0 weeks
this is two points  (0,13.4) and (4,17).


Similarly for the Saint Bernard, the two points would be  (0,6) and (4,12.4).


If you look at growth and mass specifications for these breeds you can judge if the data in your problem description make sense.




Finding equations of lines
-
Border Collie
{{{m=0.9}}};
{{{y=0.9x+13.4}}}
-
Saint Bernard
{{{m=6.4/4=1.6}}}
{{{y=1.6x+6}}}
-


RED for border collie
GREEN for saint bernard
{{{graph(400,400,-2,19,-2,26,0.9x+13.4,1.6x+6)}}}


About 10.5 weeks until both are about 22.9 kg
(find by equating the two expressions, 0.9x+13.4=1.6x+6)