Question 1067126
Original triangle
base b
height h
base b=h-3
area {{{(1/2)(h-3)h}}}



Increased base, new triangle
area  {{{(1/2)(h-3+6)h}}}
{{{(1/2)(h+3)h}}}



New triangle is area 30 square feet more.
{{{highlight_green((1/2)(h+3)h-(1/2)(h-3)h=30)}}}


{{{h^2+3h-(h^2-3h)=60}}}
{{{6h=60}}}
{{{highlight(h=10)}}}
-
{{{b=h-7}}}
{{{highlight(b=7)}}}