Oh, this will be very nice for elimination:
L + W =35
2L + 1,5W = 62
Double the first equation and subtract,
This eliminates the variable W...and you should be able to get the answer from there.
Please note: For elementary systems of equations such as this, I usually find elimination to be the easiest.
In this case you have been asked to use elimination, but be aware that there are several other methods.