Answer:
![\boxed {\boxed {\sf v=28 \ mL}}](https://img.qammunity.org/2021/formulas/chemistry/high-school/32ui20wmid0a2fyatvewk036ry0jb6x1e9.png)
Step-by-step explanation:
Jason found the volume of the marble using water displacement.
To calculate the volume, we must subtract the initial volume from the final volume.
![v_f-v_i](https://img.qammunity.org/2021/formulas/chemistry/high-school/e2zrzp4g7g2o676j75nvfzv5r2i8mvc5ii.png)
The initial or original volume is 50 milliliters.
The final volume, after the marble is added to the water, is 78 milliliters.
![v_f=78 \ mL\\v_i=50 \ mL](https://img.qammunity.org/2021/formulas/chemistry/high-school/xg9zn5szrba6ocjhlb0lmst4v84xqtrv8j.png)
Substitute the values into the formula and subtract.
![78 \ mL-50 \ mL](https://img.qammunity.org/2021/formulas/chemistry/high-school/9d3u85jtuicnvsmjt4rk2ed38e4js8f0em.png)
![28 \ mL](https://img.qammunity.org/2021/formulas/chemistry/high-school/gx1lj1lwo3jucg5e9tgax55uhr0morua10.png)
The volume of the marble is 28 milliliters.