According to the question statement, the total sum of students is 221, which includes the students that ride on bus and the students that ride in a van.
The students that ride in a van are five, the students that ride on bus are 6 times s which is the product of the number of buses and the number of students that are on each bus.
Write all this information into an equation, this way:

Now, solve the equation for s to find the number of students that are on each bus.

There are 36 students on each bus.
Answer: x = 2
Step-by-step explanation:

Replace y in the first equation by the value of y in the second equation.

Answer:
99
Step-by-step explanation:
You can solve it by Squaring/multiply 18 by itself and 15 by itself then subtract them both:
(18 × 18) - (15 × 15)
324 - 225
99
You could also do difference of two squares:
(x² - y²)
= (x + y) (x - y)
= (18 + 15) (18 - 15)
= (33) (3)
= 99
Answer:
I think it's A, but I'm not sure :)
Sn=(a1)((1-r^n)/(1-r))
=(-11)(1-(-4)^7)/(1-(-4))
=(-11)(1-(-16384))/5)
=(-11)(3277)
=-36047