Are you serious? This is addition and subtraction.
If she has $45 dollars to spend...
17+8+4=29. <------ This is the total of dollars she spent (admission, clothing, etc.)
$45-$29= $16 (This is what she has left)
For a positive expression just do
10+6=16 Boom! Done.
2nd problem)
She has $16 dollars left. The shirt is $19. NO she cannot buy the shirt because 16-19 is -3. You can't do $45, and start over because she already spent her money. Therefore, No she cannot.