$45 per plumber hour (p)
$25 per assistant hour (a)
$4035 = 25a + 45p
p = 2a
4035 = 25a + 45(2a)
4035 = 25a + 90a
4035 = 115a
a = 35.086 hours
p = 2(35.086)
p = 70.174 hours
The plumber worked about 70 hours, and his assistant worked about 35 hours.
50=t/2+8
50-8=t/2
42=t/2
2×42=t
84=t
check: 50=84/2+8
50= 42+8
50=50