If (x, 4) lies on the line 3x+y=10, we can just substitute the values in
x=x and 4=y
3x+4= 10
Subtract 4 from each side
3x= 6
Divide by 3 on each side
x=2
so the x in (x,4) must be 2
(n / 10) + 15
The quotient is the result of division between two numbers
If the plant grows 0.4 cm per week....in 3 weeks, it will have grown :
3 * 0.4 = 1.2 cm
Morse code is essentially the same as binary. That is, there are two "digits", a dot or a dash.
There are 26 letters in the English alphabet. Clearly, we can't just use one dot or dash, since that could only encode 2 letters at the most. We can't use two symbols because that could only encode 4 letters at the most. Similarly, 3 symbols means

letters at most.
We have to select the smallest power of 2 that exceeds or is equal to 26. In this case,

, so we would have to use up to 5 symbols to encode each letter in the alphabet.