Question 931198
1. x Rob's age
x-5 = (4x-5) - 30, x = 10, Rob's age. His father is 40{{{4*10}}}.   And... 5 = 35 - 30
......
2. x Alex's age
x - 3 = 1/3(x+8 - 3) + 2
3x-9 = x + 5 + 6 
2x = 20
x = 10, Alex's age.  Tom 18 {{{10+8}}}
and...
7 = 5 + 2
........
x Mary's age
2x - 5 = 3(x-5) - 10
2x - 5 = 3x - 15 - 10
20 = x, Mary's age.  John 1s 40 {{{2*20}}}
And...
35 = 45 - 10