Firstly, understand prefixes :)
giga 1000000000
mega 1000000
kilo 1000
deci 0.1
centi 0.01
milli 0.001
micro 0.000001
nano 0.000000001
X=number total of student at the school.
70% of x=161
can suggest this equation:
(70/100)x=161
0.7x=161
x=161/0.7=230
Answer: the school has 230 students