Because in the numerator and denominator of the fraction 1a/3a, you're able to simplify that and get 1/3. There is actually no solution to the problem you're asking. You're unable to find out what (a) equals.
is this edginuity
...................... i needed more words
I'm pretty sure it's 70 because they have to intersect at right angles, and 70 + 20 = 90.