Answer:
Step-by-step explanation:
we know that
<em>step 1</em>
<em>Brian can lay a slab of concrete in 6 hours</em>
so
The 100% -------> in 6 hours
using proportion
Find in an hour how much percentage Brian can execute
<em>step 2</em>
<em>Greg can lay a slab of concrete in 4 hours</em>
so
The 100% -------> in 4 hours
using proportion
Find in an hour how much percentage Greg can execute
step 3
we know that
In one hour (Brian and Greg) execute (16.67%+25%)=41.67%
so
by proportion
Find out how long it will take Brian and Greg to lay a concrete slab working together