zsolve: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/lib64/4ti2/bin/zsolve - from package: 4ti2

You may install the required package with command yum install {package}

Error in other languages:
zsolve: bevel nie gevind nie
zsolve: comandă negăsită
zsolve: comando não encontrado
zsolve: commande introuvable
zsolve: command not found
zsolve: käsku ei ole
zsolve: không tìm thấy lệnh
zsolve: komanda nerasta
zsolve: Kommando nicht gefunden.
zsolve: kommandot finns inte
zsolve: komut yok
zsolve: nie znaleziono polecenia
zsolve: níor aimsíodh an t-ordú
zsolve: no se encontró la orden
zsolve: no s'ha trobat l'ordre
zsolve: opdracht niet gevonden
zsolve: parancs nem található
zsolve: perintah tidak ditemukan
zsolve: príkaz nenájdený
zsolve: příkaz nenalezen
zsolve: команда не найдена
zsolve: командата не е открита
zsolve: 命令找不到
zsolve: コマンドが見つかりません