Check your school profile, it may provide a conversion chart. At my kids’ school (which gives number grades like your school), the chart is as follows:
A+ / 97-100 / 4.0
A / 93-96 / 3.7
A- / 90-92 / 3.5
B+ / 87-89 / 3.3
B / 83-86 / 3.0
B- / 80-82 / 2.7
C+ / 77-79 / 2.5
C / 73-76 / 2.0
C- / 70-72 / 1.7
D+ / 67-69 / 1.5
D / 65-66 / 1.0
Failure
It can vary from school to school, but this should give you a rough idea.