At the greenhouse, 1 ivy plant and 4 ferns cost $15.70. three ivy plants and 6 fern cost $26.28.

The complete question is
At the greenhouse, 1 ivy plant and 4 ferns cost $15.70. Three ivy plants and 6 fern cost $26.28. What is the cost of each plant and each ferns?

let 
x-------------> the cost of each ivy plant
y-------------> the cost of each ferns

we know that
x+4y=15.70-------> equation 1
3x+6y=26.28-----> equation 2

using a graph tool
see the attached figure

the solution is 
x=1.82
y=3.47

the answer is
the cost of each ivy plant is $1.82
 the cost of each ferns is $3.47