physics
posted by sima .
A steel rod of length 4 m is welded to the end of an aluminum rod of length 3 m (lengths measured at 23 °C). The combination rod is then heated to 198 °C. What is the length of the combination rod at 198 °C? (The linear expansion coefficients for steel and aluminum are 1.3 105 °C−1 and 2.2 105 °C−1, respectively. Enter your answer to three significant figures.)
I know the equation to be used is, delta length=(linear coefficient of expansion)(length)(delta temperature)
i am confused as to what to use for length on the right side of the equation, and what to subtract from delta length

Hmmm. Do it in two parts, steel expansion, and aluminum expansion, then add the two expansions.

What do i use for delta length?

That is what you are solving for.
deltaLengthAl= coeff*changetemp*lengthorigAl
deltaLengFe= coeff*changetemp*lenghorigFe
Total changelenght= sum of above 
it didn't give me the correct answer