Then re-write using approximate decimal values, so that you can use a calculator:
Trial and error will show you which values of to use in your two formulae, to work out values of . But if you use values of from to in steps of , that should work OK.
Plot the two graphs on the same diagram (they're both straight lines), and read off their point of intersection. (The answer, that I found algebraically, is approx. .)
(b) I assume that the first equation is . Again, trial and error will show you which values of to use. If you try to in steps of , that should be OK.
Again, plot the two graphs on a single diagram. This time, one is a curve and the other turns out to be a tangent to the curve. Read off the values of and where the tangent touches the curve. An algebraic method tells me it is .