Consider the given monomials. Let us determine the sum of these monomials,
1.
![-15u^3+5u^3](https://img.qammunity.org/2019/formulas/mathematics/high-school/nko6wlb6lj9a2d7chxbxi04ufpbx30dwxd.png)
=
![-10u^3](https://img.qammunity.org/2019/formulas/mathematics/high-school/2ptdcu56tqwypze72uai3xu8mflq81tkmg.png)
Therefore, the sum of the given monomials is
.
2.
![10u^3+(-5u^3)](https://img.qammunity.org/2019/formulas/mathematics/high-school/x5lndfvod5w0qoue4jny0iw0taipnszj4b.png)
=
![10u^3-5u^3](https://img.qammunity.org/2019/formulas/mathematics/high-school/grb8cf999rpgrexfh1e3b0194cj8x28no3.png)
=
![5u^3](https://img.qammunity.org/2019/formulas/mathematics/high-school/y81j9a1axtbyhlijcjn4afwufgsoqyrwa3.png)
Therefore, the sum of the given monomials is
.
3.
![10u^3+5u^3](https://img.qammunity.org/2019/formulas/mathematics/high-school/n565z3f1bnbjhqm9hxf0v24bpsjqqpwx17.png)
=
![15u^3](https://img.qammunity.org/2019/formulas/mathematics/high-school/epyg0jfimfo134xo4hytj75yaspjyj9lxw.png)
Therefore, the sum of the given monomials is
.
4.
![5u^3+(-10u^3)](https://img.qammunity.org/2019/formulas/mathematics/high-school/35f0z98nygzitsef4lny00rkyrsv8z94y6.png)
=
![5u^3-10u^3](https://img.qammunity.org/2019/formulas/mathematics/high-school/zdo2tcrix0xpnftykpm72ik05j1ssx48ip.png)
=
![-5u^3](https://img.qammunity.org/2019/formulas/mathematics/high-school/5882oic7e0n3cujup2ljlaec5zfl65df0u.png)
Therefore, the sum of the given monomials is
.