Hello! :)

Use a proportion to find how many seconds are needed to fold 5 shirts.
We are given that he takes 28 seconds to fold 2 shirts:
28 sec : 2 shirts
We are not given the amount of time needed for 5 shirts, which we need to solve:
x seconds : 5 shirts
Express in a fraction:

Cross multiply and simplify:

Therefore, he needs 70 seconds to fold 5 shirts.
Answer:
14
Step-by-step explanation:
Since S is the midpoint of RT, then RS = ST
RS = RT - ST = (3x + 7) - (x + 7) = 3x + 7 - x - 7 = 2x
so we get that RS = 2x
but since RS = ST, and RS=2x & ST=x+7
then 2x = x + 7
2x-x = 7
x = 7
ST = x+7 = 7+7 = 14
P.S. Hope it makes sense. If you have any questions, feel free to ask them in the comments senction. I'll be happy to help. Have a wonderful day!