How nice of them to GIVE us the system of equations !
This thing has already almost solved itself.
3j  +  5p  =  7.60
  j  +  2p  =  2.90
Write both equations again, but this time, 
multiply each side of the second one by  3 :
3j  +  5p  =  7.60
3j  +  6p  =  8.70
Now subtract the top equation from the bottom one:
  
 0  +  p  =  1.10
and Bada-Bing ... There's the cost of the pancake special ...  p = $1.10 .
We can take the second original equation now:
  j  +  2p  =  2.90
Subtract one ' p ' from each side:
  j  +  (2p - 1p)  = (2.90 - 1.10)
  j  +    p      =   $1.80
There's your bill for one juice and one pancake special.  
Notice that the juice is only  70 cents.
They didn't ask us for that.