How many raspberry pis would be needed to equate torun a cur

How many raspberry pi\'s would be needed to equate to/run a current computer with the following specs

i7-4510U CPU @ 2.00 GHz 2.60 GHz

8.00 GB RAM

64 bit operating system

Solution

not to be sure but we can predict by assumption almost 18-20 pi will be needed to run a same process of i7 on same time. some sources says Pi2 is almost 18 times slower than the 17 and all its core;s are not gonna work at same time .