$80
1) In this problem, we can the following:
First + Second + Third = 160
First= Second+3rd Card
2) We can set the following:
[tex]\begin{gathered} 2x+20+\left(x+20\right)+x=160 \\ \\ 4x+40=160 \\ \\ 4x+40-40=160-40 \\ \\ 4x=120 \\ \\ \frac{4x}{4}=\frac{120}{4} \\ \\ x=30 \\ \\ First\:card: \\ \\ 2x+20 \\ \\ 2(30)+20 \\ \\ 60+20 \\ \\ 80 \\ \end{gathered}[/tex]3) Thus, the first card cost $80