Find the least number which when added to $624$ makes it a perfect square?

Each students in the class contributed as many rupees as the number of students in the class for a picnic. The school contributed rupees $150$ per teacher who led the trip. If the total amount collected was rupees $1350$ and the number of teachers who led the trip was $3$, how many students were there in that class?

In a class, each boy contributed as much paise as the number of boys to purchase a gift costing$₹13$. If the teacher's contribution is$₹4$, then the number of boys in the class is:

There are two grades A and B of workers in a workshop. Every worker contributes as many rupees as there are workers of his own category, If the total amount contributed is rupees $196$, including rupees $16$ Contributed by the owner of the workshop, what is the total number of workers in that workshop?

In the following question, what will come in place of a question mark?

$\sqrt{?\times 7} \times 18 = 84$