Answer:
The measure of QS is 68 units.
Explanation:
Given information: R is midpoint of QS, RS=2x-4, ST=4x-1, and RT=8x-43.
We need to find the value of QS.
From the given figure it is clear that points Q, R, S and T are collinear.
![RT=RS+ST](https://img.qammunity.org/2019/formulas/mathematics/middle-school/m9ajigqye0mqcaee2i00ekt694tscrxm2v.png)
![8x-43=(2x-4)+(4x-1)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/7zv8vui5b0qnxryvo1zksakaz3agpbuh3n.png)
On combining like terms.
![8x-43=(2x+4x)+(-4-1)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/aiuadpmawskwco3kuazbhfkg9w0gp81v45.png)
![8x-43=6x-5](https://img.qammunity.org/2019/formulas/mathematics/middle-school/dt123m1ghej9devyt0ghpmm68u129t884e.png)
Isolate variable terms.
![8x-6x=43-5](https://img.qammunity.org/2019/formulas/mathematics/middle-school/qjv8ah8tkporedlj5q7bvdhazr79ynii5u.png)
![2x=38](https://img.qammunity.org/2019/formulas/mathematics/middle-school/w7xtnl016jeui3fsglhpggj1bnau2zy2py.png)
Divide both sides by 2.
![x=19](https://img.qammunity.org/2019/formulas/mathematics/high-school/9t3skpfqqv73yfttpcapxx6s3ldueky94j.png)
The value of x is 19.
It is given that R is midpoint of QS. It means R divides the line QS in two equal parts.
![QS=2(RS)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/d3o87fth7w6e8xoyzn5r32vyfzqqncbogh.png)
![QS=2(2x-4)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/v7uwm9q0rts30o9uvoeiilkjmx1psrvrp6.png)
Substitute x=19 in the above equation.
![QS=2(2(19)-4)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/xemb84gs9v84k7owi3idblzcidvuh7q9de.png)
![QS=2(38-4)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/a10jji9e3ta6b9jpdljaypupwakyec6zl6.png)
![QS=2(34)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/eajm2vdi66c9w52519yycb7kr8wai1254d.png)
![QS=68](https://img.qammunity.org/2019/formulas/mathematics/middle-school/9zjppx9l3e5r3gbioe1z28636mrzoxodrv.png)
Therefore the measure of QS is 68 units.