Answer:
20.
Step-by-step explanation:
1) according to the condition RT=ST+RS;
2) if RT=4x, ST=3x-8; RS=4x-7, then it is possible to re-write the equation as:
4x=(3x-8)+(4x-7);
3) if to solve this equation, then:
4x=7x-15; ⇔ 3x=15; ⇔ x=5.
4) if x=5, then the length of RT is:
RT=4x=20.
