Answer :
Let x be the number of three credit classes. The total credits for this classes will be:
[tex]3x[/tex]Now, we know he already has 70 credits, that means that the total is:
[tex]3x+70[/tex]Now this has to be al least 120, that means that we have the inequality:
[tex]3x+70\ge120[/tex]Solving for x we have:
[tex]\begin{gathered} 3x+70\ge120 \\ 3x\ge120-70 \\ 3x\ge50 \\ x\ge\frac{50}{3} \\ x\ge16.67 \end{gathered}[/tex]Now, since Jovanny can't take a fraction of a class he need to take 17 three credit classes.