Can you please help me solve this:
t + u = 7
10t + u + 9 = 10u + t
10t-t+u-10u=-9
9t-9u=-9
9(7-u)-9u=-9
63-9u-9u=-9
-18u=-9-63
u=9
t+u=7
t+9=7
t=7-9
t=-2