Okay, here we have this:
Considering the provided information, we are going to calculate the requested dimensions, so we obtain the following:
According to the information given then we have:
Area=90 cm²
Base=x
Altitude=2+2x
And replacing in the area formula then we have the equation to solve:
Area=(Base*Altitude)/2
90 cm²=(x*(2+2x))/2
90=(2x+2x^2)/2
180=2x+2x^2
2x+2x^2-180=0
2(x-9)(x+10)=0
x-9=0 or x+10=0
x=9 or x=-10
Finally we only consider the value of x positive because the measurements can only be positive, so we finally get
Base=x=9 cm
Altitude=2+2x=2+(2*9)=2+18=20 cm
Finally we obtain that the length of the base is 9cm and the altitude is 20 cm.