The identity property of addition states that a + 0 = a
Your answer is identity property of addition.
Its 1081
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Given problem is 
To simplify that we need to multiply and divide by conjugate of the denominator
conjugate of denominator 6+i will be 6-i as we just need to change sign of the imaginary part
Now multiply and divide by 6-i







Hence final answer is 
Hello,
Let's assume x the time the express runs.
56*x=35*(1.5+x)
==>21x=52.5
==>x=2.5 h =2 h 30 min
1.Direct variation
2.Not sure