No these triangles are not similar.
Step-by-step explanation:
Given Information on First triangle :
Base = 3
Height = 8
Given information on Second triangle :
Base = 4
Height = 10
Area of a Right Angle triangle :
[tex] \frac{base \times height}{2} [/tex]
Area of First triangle :
[tex] \frac{3 \times 8}{2} = \frac{24}{2} \\ \\ = 12[/tex]
Area of Second triangle :
[tex] \frac{4 \times 10}{2} = \frac{40}{2} = 20[/tex]
Their Ratio :
[tex]12:20 = \frac{12}{20} \\ = \frac{3}{5} [/tex]
So I guess no, the triangles are not similar.
