Depending on the algebra problem, you'll need to know some geometry. The following represents some of the most common shapes in geometry and their formulas for perimeter, area, volume, surface areas, and circumference:

Two-Dimensional Shapes
Shape Perimeter/Circumference Area
Rectangle P = 2(l + w) A = lw
Square P = 4s A = s2
Triangle P = a + b + c A = 1/2bh
Trapezoid P = a + b1 + c + b2 A = 1/2h(b1 + b2)
Isosceles Trapezoid P = 2w + b1 + b2 A = 1/2h(b1 + b2)
Circle C = πd = 2 π r A = π r2
Three-Dimensional Shapes
Shape Surface Area Volume
Box SA = 2lw + 2lh + 2wh V = lwh
Sphere SA = 4 π r2 V = 4/3 π r3
Cylinder SA = 2 π r(r + h) V = π r2h