could you please correct these two problems?

marginal cost for a determined product is MC=3x+50 and the production of 20 units results in a total cost of $2,000, what is the total cost function?

Integrate MC to get

3/2² + 50x + c

Substitute to find c:

2(400) + 2(20) + c = 2,000

800+40 = 2,000

c= 1,160

3/2² + 50x + 1,160

2- If consumption is $5.8 billion when disposable income is 0, and if the marginal propensity to consume is dc/dy = 1/√(y+9) +0.8

(in billions of dollars) find the national consumption function.

If "y" is disposable income [not national] then:

C = ƒ(y)

MPC = ∂C/∂y

C = ∫ [∂C/∂y] ∂y = ∫ [0.8+1/√(y+9)] ∂y = X + 0.8•y + 2•√(9+y)

C [billions] = X + 0.8•y + 2•√(9+y)

C[y=0] =5.8 billion

5.8 = X + 0.8•0 + 2•√(9+0)

5.8 = X+6

X = 5.8-6 = -0.2

C [billions] = 0.8•y + 2•√(9+y) - 0.2

thank you.