Yard Pennant

Triangle/Height Question… I really don’t understand these kinds of questions? Please help?

The garys have a triangular pennant of area 420 in^2. flying from the flagpole in their yard. The height of the triangle is 10 in. less than 5 times the base of the triangle. What are the dimensions of the pennant?

A = bh/2

420 = b(5b-10)/2

840=b(5b-10)
840 -5b^2 +10b = -5b^2 +10b +840 = 5(-b^2 +2b +168 ) = -5(b-14)(b+12)

b = 14
h = 60

Jermaine Pennant 39 Yard Free Kick