Instead of doing it for you, I'll do one exactly like yours step by step:
Five times the tens digit of a certain 2-digit number is 3 more than eight times the units digit.
The difference between the given number and the number obtained by reversing the digits is
six less than three times the sum of the digits. Find the number.
t = the tens digit
u = the units digit
10t+u = the number
10u+t = the number obtained by reversing the digits.
Simplify the second equation
10t + u - (10u + t) = 3(t + u) - 6
10t + u - 10u - t = 3t + 3u - 6
9t - 9u = 3t + 3u - 6
6t - 12u = -6
Divide through by 6
t - 2u = -1
Solve for t
t = 2u - 1
Substitute in
5t = 8u + 3
5(2u - 1) = 8u + 3
10u - 5 = 8u + 3
2u = 8
u = 4
Substitute in
t = 2u - 1
t = 2(4) - 1
t = 8 - 1
t = 7
The number is 74.
Now use this as a model to solve yours by.
Edwin