First, convert all measurements to inches.
Box 1:
3ft(12in)=36in+6in=42in
Box 2:
4ft(12in)=48in+10in=58in
Box 3:
4ft(12in)=48in+5in=53in
Now, add the heights together.
42in+58in+53in=153in
Finally, convert added height to feet.
153in/12in=12 with a remainder of 9, so your final answer is 12ft 9in
