The error is in line 3.
Specifically, the error is when the student went from
to simply
without a square root over top. The
should simplify to 3.
Here's what the student should have done in terms of a step-by-step picture.
![\underline{\text{Line 1:}} \ \ \ 2√(45)-3√(5)\\\\\underline{\text{Line 2:}} \ \ \ 2√(9)*√(5)-3√(5)\\\\\underline{\text{Line 3:}} \ \ \ 2*3*√(5)-3√(5)\\\\\underline{\text{Line 4:}} \ \ \ 6√(5)-3√(5)\\\\\underline{\text{Line 5:}} \ \ \ 3√(5)\\\\](https://img.qammunity.org/2023/formulas/mathematics/high-school/7ss1lbiynfaia3zrnh4cumgjczpz32zxk6.png)
The simplified final answer is
![3√(5)](https://img.qammunity.org/2023/formulas/mathematics/high-school/8mvvun4bpndql397197kc677agi1ubod2k.png)