Question 992181
She travels at 45 for t hours. That means she travels (10-t) hours at 55.

so
{{{Distance = DistanceAt45 + DistanceAt55}}}
{{{Distance = 45*t  + 55*(10-t)}}}
{{{Distance = 45t + 550 - 55t}}}
{{{Distance = 550 - 10t}}}