Among critical path activities A$-$B$-$C$-$E$-$F$-$G$-$H$,$ lowest crash slope is for activity H $($$$4).$ Maximum crashing of $3$ hours is possible for activity H$.$ So$,$ we will first crash activity H by $3$ hrs$.$ New project duration $34-3=31$ hours. Crashing cost $=4*$$$3=$ $$12.$ Critical path will remain same A$-$B$-$C$-$E$-$F$-$G$-$H$.$

Next activity with lowest crash slope on critical path is activity C $($$$5).$ Maximum crashing of $1$ hour is possible for activity C$.$ So$,$ we will crash activity C by $1$ hr$.$ New project duration is $31-1=30$ hours. Crashing cost $=$ $$12+$ $$5=$ $$17.$ Critical path will remain same A$-$B$-$C$-$E$-$F$-$G$-$H$.$

Next activity with lowest crash slope on critical path is activity E $($$$7\mathrm{.}5).$ Maximum crashing of $2$ hours is possible for activity E$.$ So$,$ we will crash activity E by $2$ hrs$.$ New project duration is $30-2=28$ hours. Crashing cost $=$ $$17+$ $$7\mathrm{.}5*2=$ $$32.$ Critical path will remain same A$-$B$-$C$-$E$-$F$-$G$.$

Next activity with lowest crash slope on critical path is activity B $($$$8).$ Maximum crashing of $1$ hour is possible for activity B$.$ So$,$ we will crash activity B by $1$ hr$.$ New project duration is $28-1=27$ hours. Crashing cost $=$ $$32+$ $$8=$ $$40.$ Critical path will remain same A$-$B$-$C$-$E$-$F$-$G$.$

Next activity with lowest crash slope on critical path is activity G $($$$15).$ Maximum crashing of $1$ hour is possible for activity G$.$ So$,$ we will crash activity G by $1$ hr$.$ New project duration is $27-1=26$ hours. Crashing cost $=$ $$40+$ $$15=$ $$55.$ Critical path will remain same A$-$B$-$C$-$E$-$F$-$G$.$