Answer: See explanation
Step-by-step explanation:
You didn't say what you'll like to calculate but let me help out.
Fourth year = 129 project.
Tenth year = 207 projects
We can form this into an arithmetic progression
Tn = a + (n-1)d
4th year = a + 3d = 129 ........ i
10th year = a + 9d = 207 ....... ii
Subtract equation i from equation ii
6d = 78
d = 78/6 = 13
This means that 13 new projects are added every year
For the first year, the number of projects done was:.
a + 3d = 129
a + 3(13) = 129
a + 39 = 129
a = 129 - 39 = 90
She worked on 90 projects in the first year.
