Alg III Uniform Motion Help

[RVCA123]

So if Lara and her mom have a fight. Lara knows that if she sticks around she might say something she shouldn't so she jumps in her car and heads west at a speed of 40 mph. Two hours later, her mom decides she had better go after her daughter. So she jumps in her car and takes off at a speed of 90 mph. How long after Lara left will it be when her catches up with her?

I let x = time of Lara's departure
x+2 = time of mom's departure

Setting it up as 40x=90(x+2)

Getting 3.6 hours. Is this correct?

 

[HallsofIvy]

You start by saying x is the "time of Lara's departure". You then say you got an answer of "x= 3.6". So what does that mean? That Lara left at 3:36? PM or AM? In any case there is nothing in the problem that allows you to say what the "time of departure" of Lara was. And, of course, multiplying the time lara left by her speed doesn't give you anything reasonable. It would be better to let x be the number of hours Lara drove. But in that case, the time her mother drove would NOT be "x+ 2". (And solving "40x= 90(x+ 2)" does NOT give you "x= 3.6".)