In ∆DEF, if m∠E is one more than three times m∠F and m∠D is three more than seven times m∠F, find the m∠D.

mD=115, mE=49, mF=16

Step-by-step explanation:

DEF is a triangle and were told to find angle measures.

If m∠E is (3F+1) and m∠D is (7F+3)

Use T-angle sum theorem and plug previous terms 7F+3+3F+1+F=180 which give F=16. Then substitute F=16 with angles D and E to find last results.

2.2°  

step-by-step explanation:

let θ = the angle of elevation.

tanθ =77/2020

tanθ = 0.038 12

      θ = tan⁻¹0.038 12

      θ = 2.2°

the surface area is 124cm²

step-by-step explanation:

length: 4cm

width: 9cm

height:   2cm