Help with solving Digit Problems (Algebra)

ok so i need help with these few problems in my hw. can u please explain it?

I know that:
t=tens
u=units
10t+u=value
10u+t=reversed

5) the tens digit of a two-digit number exceeds the units digit byt 2. The sum of the tens digit and twice the units digit is 17. Find the number

6) The units digit of a two-digit number exceeds three times the tens digit by 3. if the tens digit is subtracted from the units digit, the difference is 7. find the number/

the other few are like the ones above so please help! thank you ! :)

Problem 5
========
You don't need to write either number as 10*t + u to solve it. It's as though you were looking at two different numbers between 0 and 9 for the units and 1 to 9 for the tens.\

t - u = 2
t + 2*u = 17

Subtract these two equations.

-3u = -15
u = 5

t - u = 2
t - 5 = 2
t = 7.

75 is the actual number.

Problem 6
========\
u - 3*t = 3
u - t = 7

Again subtract them
-2t = - 4 divide by 2
-t = -2 divide by -1

t = 2
u - 3*2 = 3
u -6 = 3
u = 9

all i know is that in these types of questions u have to have 2 equations and then substitute one equation into another by the use of variables