The area of a triangle is:
A= 30mm
h= 6mm
[tex]\begin{gathered} A=\frac{b(h)}{2} \\ \\ 30=\text{ }\frac{b\lparen6\rparen}{2} \\ \\ 30\text{ \lparen2\rparen = 6b} \\ \\ 60=\text{ 6b} \\ \\ \frac{60}{6}=\text{ b} \\ \\ 10=\text{ b} \end{gathered}[/tex]The base of the triangle is 10mm