basic math
posted by mike .
A computer can execute 36 instructions per microsecond.
How many instructions can it execute in 4 min?

36/microsec.
36/microsec x (10^6 microsec/sec) x ((60 sec/min) x 4 min = 8 something times 10^9.
or you can look here.
http://www.algebra.com/algebra/homework/Lengthanddistance/Lengthanddistance.faq.question.67226.html