The first step is to define the system of equations.
Take x and y as the cost of a small box and a large box respectively.

Solve the system.



A small box costs $4 and a large box costs $4 too.
cos(6x) = 0
cos⁻¹[cos(6x)] = cos⁻¹(0)
6x = 90
6 6
x = 15°
x = ¹/₁₂π radians
cos(6x) = 0
<span>cos⁻¹[cos(6x)] = cos⁻¹(0)
</span> 6x = 270
6 6
x = 45
x = ¹/₄π radians
cos(6x) = 0
<span>cos⁻¹[cos(6x)] = cos⁻¹(0)
</span> 6x = 450
6 6
x = 75
x = ⁵/₁₂π radians
Answer:
Number of sent mail = 36
Number of received mail = 75
Step-by-step explanation:
Let,
x be the number of mails sent
y be the number of mails received
According to given statement;
x + y = 111 Eqn 1
y = 2x + 3 Eqn 2
Putting value of y from Eqn 2 in Eqn 1
x + 2x + 3 = 111
3x = 111 - 3
3x = 108
Dividing both sides by 3

Putting x = 36 in Eqn 2
y = 2(36) + 3
y = 72 + 3 = 75
Hence,
Number of sent mail = 36
Number of received mail = 75