Reconstruction of a signal using an ideal DAC
This is an ill posed question. 

First it doesn't talk about the output DAC reconstruction sampling rate which is necessary for the reconstruction filter design and which also determines the frequency spectrum scaling of the reconstructed signal. Anyway then you may assume the DAC sampling-rate to be equal to ADC sampling rate for simplicity, which are both $F_s = 100$ Hz in your case. (btw your matlab code is wrong here, you have taken the sampling period to be $0.001$ which should be $0.01$.)

Furthermore, it talks about an ideal DAC which cannot be realized by any code, but, its output can be mathematically described perfectly without any computation by definition of the ideal DAC to be $$y_r(t)=x_c(t)$$ as long as there is no aliasing during the ADC stage which is the case here. So it's not clear if they want you to actually compute an approximate output $y_r(t)$ or simply evaluate the exact described output $x_c(t)$ in terms of input samples, which is a null computation.