tan(a+b)=3/4,tan(a-π/4)=1/2
tan(b+π/4) = tan[(a+b)-(a-π/4)]
= [tan(a+b)-tan(a-π/4)]/[1+an(a+b)tan(a-π/4)]
= [3/4-1/2]/[1+3/4*1/2]
= (1/4)/(11/8)
= 2/11