Economics question. How do I find out the entire line if I am only given to points on the budget line?

up09: Economics question. How do I find out the entire line if I am only given to points on the budget line?
Martha is preparing for exams in economics and sociology.She has time to read 40 pages of economics and 30 pages of sociology.In the same amount of time she could also read 30 pages of economics and 60 pages of sociology.

(a)Assuming that the number of pages per hour that she can read of either subject does not depend on how she allocates her time, how many pages of sociology could she read if she decided to spend all of her time on sociology and none on economics?

Answers and Views:

Answer by Bored Goblin
a+b40=30
a+b30=60

solve for a and b.
e.g. express a from 1st eq., and plug into 2nd.