Spaceship model kits originally cost d dollars online. You buy cach kit on sale for 30% of the original price, plus a shipping fee of $3.50 per kit. After
assembly, you sell each model online for (2.50 + 5) dollars. What is your
profit on each model spaceship sold?

the graph on the bottom right

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this

x = -4

step-by-step explanation:

- 20 - 4(x + 3) = 4x

=> -20 - 4x - 12 = 4x

=> - 32 -4x = 4x

=> -32 = 4x + 4x

=> - 32 = 8x

=> -32/8 = x

=> -4 = x