Answer
$108 for labor estimate
Work Step by Step
Marcus: 6 hours to lay slab (1/6 of slab in 1 hour)
Tony: 4 hours to lay slab (1/4 of slab in 1 hour)
$1/6 + 1/4 = 1/x$
$12(1/6 + 1/4 = 1/x)$
$2 + 3 = 12/x$
$5=12/x$
$5*x/5 =12/x*x/5$
$x = 12/5$
$12/5 * 45$
$12/5 * 9*5$
$12 * 9=108$
