Answer:
He completed 13 courses worth 3 credits and 5 courses worth 4 credits.
Step-by-step explanation:
Let
Number of courses worth 3 credits = x
Number of courses worth 4 credits = y
1. The student completed a total of 18 courses, then
[tex]x+y=18[/tex]
2. The student earned a total of 59 credits, he earned 3x on 3 credits' courses and 4y on 4 credits' courses, so
[tex]3x+4y=59[/tex]
3. You get the system of two equations:
[tex]\left\{\begin{array}{l}x+y=18\\ \\3x+4y=59\end{array}\right.[/tex]
From the first equation
[tex]x=18-y[/tex]
Substitute it into the second equation:
[tex]3(18-y)+4y=59\\ \\54-3y+4y=59\\ \\4y-3y=59-54\\ \\y=5\\ \\x=18-5=13[/tex]
He completed 13 courses worth 3 credits and 5 courses worth 4 credits.
