Question 1204475
Draw a picture of the wall. Note that since the arrangement on the wall is symmetrical, you really only need a picture of half of the wall.

To find how far from the wall the nail closest to the wall will be


|...........................................{{{78.4}}}..................................|
..........................................{{{39.2}}}
<--------------------------|


1) half of {{{78 &2/5= 78.4}}}=>{{{78.4/2=39.2}}} (starting point)
(2) minus half of {{{2 &3/5=2.6}}} =>{{{2.6/2=1.3}}}  (deduct half space between pictures) 
(3) minus half of {{{12 &1/2 =12.5}}} => {{{12.5=6.25}}} (deduct half length of the picture to get to its center)
(4) minus half of {{{4& 1/2=4.5}}} => {{{4.5/2=2.25}}} (deduct half of distance between nails and you will get to the position of the nail closest to the wall)

 
{{{39.2-1.3-6.25-2.25=29.4cm}}}

the first nail be placed will be {{{29.4cm}}} far from the end of the wall