This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
In order to keep up the same level of achievement, the ratio of "number of successfully completed questions" to "the number of attempted questions" should remain same.

more problems to complete = 45
let number of problems 
he need to successfully complete = x

 \frac{12}{15}= \frac{x}{45}  \\ \\x= \frac{12}{15} \times 45\\ \\ x=12 \times 3=36

He should complete 36 questions out of 45 successfully.