Because the question gives the factored runway length we can go into the right side of the graph with the given distance, 2000ft, and into the left side of the graph with the stated conditions of ISA and 4000ft. Where the two lines meet (make sure you put the wind component in) we'll get the take-off mass.
Because you've been given the factored runway length that weight will comply with the regulatory requirements. The actual runway length is 2000 x 1.15 = 2300ft.
So we'll be getting airborne in 2000ft and the additional 300ft is the safety factor.
When considering any of these type of questions look for the word required If it says calculate the landing distance required or take-off distance required then we have to use the appropriate safety factor.
One sentence of caution....the MRJT1 graphs already have the regulatory factors built in, so the application only applies to the SEP and MEP graphs.