13. xy= x times by y
14. 7/t-4= 7 divided by t take away 4
15. 22+t 2= 22 add t squared
16. 51-x= 51 take away x
17. x-y^2= x take away y squared
18. 36/12+12= 36 divided by 12 add 12
19. ab-16= a times by b take away 16
If this is what it means , I hope this helped ! :)